[Minor fixes] correct version comparison, nil-safe speaker update, and RLock/RUnlock mismatch

[siddimore]

Why

Three independent issues found during a code walk through:

• compareVersions produced wrong results for double-digit version components — the > branch used string comparison ("10" > "9" is false lexicographically) even though the < branch already used the correctly parsed integers.
• OnSpeakersChanged used reflect to detect a nil participant — assigning a *RemoteParticipant directly into a Participant interface before checking nil creates a non-nil interface wrapping a nil pointer, so a plain == nil check silently fails. Using reflect is both unusual and unnecessary here.
• getPublication held a write lock for a read-only operation — the lock acquisition was changed to RLock but defer p.lock.Unlock() was left behind, which would panic at runtime with a mismatched unlock.

What changed

File Change
utils.go Use parsed integer p1 > p2 instead of string parts1[i] > parts2[i]
room.go Check *RemoteParticipant nil before boxing into interface; remove reflect import
participant.go Fix defer p.lock.Unlock() → defer p.lock.RUnlock() to match the RLock
utils_test.go New table-driven tests for compareVersions, including the double-digit regression case

How tested

• Added TestCompareVersions in utils_test.go covering equal, greater, less, double-digit components ("10.0.0" vs "9.0.0"), and differing length versions — all pass.
• The room.go and participant.go changes are mechanical and covered by existing room/participant tests.