style: add eslint-disable comments for intentional == null checks

Added // eslint-disable-next-line eqeqeq comments for intentional null/undefined checks:
- sender-key-message.ts: checking for null OR undefined parameters
- WAM/encode.ts: checking for null OR undefined id
- baileys-event-stream.test.ts: renamed unused event parameter to _event

These changes are COSMETIC ONLY - no logic changed:
- Build still passes ✅
- All tests still work ✅
- API behavior unchanged ✅

The == null pattern is intentionally used to check for BOTH null AND undefined,
which is the correct behavior for these optional parameters.

https://claude.ai/code/session_015R3U3kiprQiNTTNNt31Sg6

src/WAM/encode.ts

@@ -78,6 +78,7 @@ function encodeEvents(binaryInfo: BinaryInfo) {
 			}
 
 			const fieldFlag = extended ? FLAG_EVENT : FLAG_FIELD | FLAG_EXTENDED
+			// eslint-disable-next-line eqeqeq
 			if (id == null) {
 				continue
 			}