perf: optimize history sync memory and CPU usage

Aligns with Baileys upstream PR #2333 (jlucaso1). Surgical port of
4 micro-optimizations + 2 test files. No collision with InfiniteAPI's
LID/PN, carousel, buttons, Bad MAC or app state sync resilience code.

Changes:

1. WAProto longToString/longToNumber: use native BigInt instead of
   Long library division loops. ~4.6x faster per call (237ns -> 52ns).
   BigInt.toString() delegates to V8 native C++. Same change applied
   to fix-imports.js (template) and index.js (generated artifact) so
   future regenerations stay in sync.

2. downloadHistory: stream-pipe createInflate instead of buffering
   the full compressed payload then inflating. Cuts RSS peak ~50%
   on 50MB history payloads.

3. processHistoryMessage: drop the { ...chat } shallow copy before
   pushing to chats[]. The decoded protobuf object is not referenced
   after the push.

4. downloadEncryptedContent transform: skip Buffer.concat when
   remainingBytes is empty (the common case — chunks usually arrive
   AES-aligned). ~19x faster per chunk (78ms -> 4ms over 25k chunks).

Tests:
- bigint-validation.test.ts (NEW): 32 parameterized cases covering
  zero, MAX_SAFE_INTEGER boundary, max int64/uint64, negative values,
  tricky bit patterns and powers of 2; plus 200-iter fuzz comparing
  old Long vs new BigInt implementations for equivalence.
- proto-tojson-long.test.ts: kept the existing fork-only test for
  string-in-Long-field graceful handling, appended 4 upstream tests
  covering Long->string fast path, large unsigned > MAX_SAFE_INTEGER,
  zero/small values and encode/decode roundtrip.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

WAProto/fix-imports.js

@@ -18,14 +18,18 @@ try {
     '\tif (typeof value === "number") {\n' +
     '\t\treturn String(value);\n' +
     '\t}\n' +
-    '\tif (!$util.Long) {\n' +
-    '\t\treturn String(value);\n' +
+    '\t// Fast path: convert Long {low, high} directly via native BigInt\n' +
+    '\t// BigInt.toString() is a native C++ operation, much faster than Long\'s pure JS division loops\n' +
+    '\tif (value && typeof value.low === "number" && typeof value.high === "number") {\n' +
+    '\t\tconst lo = BigInt(value.low >>> 0);\n' +
+    '\t\tconst hi = BigInt(value.high >>> 0);\n' +
+    '\t\tconst combined = (hi << 32n) | lo;\n' +
+    '\t\tif (!unsigned && value.high < 0) {\n' +
+    '\t\t\treturn (combined - (1n << 64n)).toString();\n' +
+    '\t\t}\n' +
+    '\t\treturn combined.toString();\n' +
     '\t}\n' +
-    '\tconst normalized = $util.Long.fromValue(value);\n' +
-    '\tconst prepared = unsigned && normalized && typeof normalized.toUnsigned === "function"\n' +
-    '\t\t? normalized.toUnsigned()\n' +
-    '\t\t: normalized;\n' +
-    '\treturn prepared.toString();\n' +
+    '\treturn String(value);\n' +
     '}\n\n'
   const longToNumberHelper =
     'function longToNumber(value, unsigned) {\n' +
@@ -33,19 +37,19 @@ try {
     '\t\treturn value;\n' +
     '\t}\n' +
     '\tif (typeof value === "string") {\n' +
-    '\t\tconst numeric = Number(value);\n' +
-    '\t\treturn numeric;\n' +
-    '\t}\n' +
-    '\tif (!$util.Long) {\n' +
     '\t\treturn Number(value);\n' +
     '\t}\n' +
-    '\tconst normalized = $util.Long.fromValue(value);\n' +
-    '\tconst prepared = unsigned && normalized && typeof normalized.toUnsigned === "function"\n' +
-    '\t\t? normalized.toUnsigned()\n' +
-    '\t\t: typeof normalized.toSigned === "function"\n' +
-    '\t\t\t? normalized.toSigned()\n' +
-    '\t\t\t: normalized;\n' +
-    '\treturn prepared.toNumber();\n' +
+    '\t// Fast path: convert Long {low, high} directly via native BigInt\n' +
+    '\tif (value && typeof value.low === "number" && typeof value.high === "number") {\n' +
+    '\t\tconst lo = BigInt(value.low >>> 0);\n' +
+    '\t\tconst hi = BigInt(value.high >>> 0);\n' +
+    '\t\tconst combined = (hi << 32n) | lo;\n' +
+    '\t\tif (!unsigned && value.high < 0) {\n' +
+    '\t\t\treturn Number(combined - (1n << 64n));\n' +
+    '\t\t}\n' +
+    '\t\treturn Number(combined);\n' +
+    '\t}\n' +
+    '\treturn Number(value);\n' +
     '}\n\n'
 
   if (!content.includes('function longToString(')) {

WAProto/index.js

@@ -12,14 +12,18 @@ function longToString(value, unsigned) {
 	if (typeof value === "number") {
 		return String(value);
 	}
-	if (!$util.Long) {
-		return String(value);
+	// Fast path: convert Long {low, high} directly via native BigInt
+	// BigInt.toString() is a native C++ operation, much faster than Long's pure JS division loops
+	if (value && typeof value.low === "number" && typeof value.high === "number") {
+		const lo = BigInt(value.low >>> 0);
+		const hi = BigInt(value.high >>> 0);
+		const combined = (hi << 32n) | lo;
+		if (!unsigned && value.high < 0) {
+			return (combined - (1n << 64n)).toString();
+		}
+		return combined.toString();
 	}
-	const normalized = $util.Long.fromValue(value);
-	const prepared = unsigned && normalized && typeof normalized.toUnsigned === "function"
-		? normalized.toUnsigned()
-		: normalized;
-	return prepared.toString();
+	return String(value);
 }
 
 function longToNumber(value, unsigned) {
@@ -27,19 +31,19 @@ function longToNumber(value, unsigned) {
 		return value;
 	}
 	if (typeof value === "string") {
-		const numeric = Number(value);
-		return numeric;
-	}
-	if (!$util.Long) {
 		return Number(value);
 	}
-	const normalized = $util.Long.fromValue(value);
-	const prepared = unsigned && normalized && typeof normalized.toUnsigned === "function"
-		? normalized.toUnsigned()
-		: typeof normalized.toSigned === "function"
-			? normalized.toSigned()
-			: normalized;
-	return prepared.toNumber();
+	// Fast path: convert Long {low, high} directly via native BigInt
+	if (value && typeof value.low === "number" && typeof value.high === "number") {
+		const lo = BigInt(value.low >>> 0);
+		const hi = BigInt(value.high >>> 0);
+		const combined = (hi << 32n) | lo;
+		if (!unsigned && value.high < 0) {
+			return Number(combined - (1n << 64n));
+		}
+		return Number(combined);
+	}
+	return Number(value);
 }
 
 export const proto = $root.proto = (() => {