feat: remove iter, improve some methods

feat: Add `Result.UnwrapUnchecked()`, and strengthen the stability of…

… `Option.UnwrapUnchecked()`.

feat: Add AssertRet

perf: Inline the NextBack method to improve performance.

feat: Add ToErrable and rename ErrFmt to FmtErr

feat: Improve throw-catch

Update sync.go

Change-Id: I3c84c9f8b5d54601db6318ac883b143caa9b9352

chore(sync): improved LazyValue method names

Change-Id: I854a8159c24bf33bfdd57c8e267e0291c760acd1

feat(sync): add RWMutex. TryBest

Change-Id: I1aa412ddab4748dfa232db808a906bab632e9206

docs: improved comment

Change-Id: Id59e60d512b03d52cf7d1f9c1a25394015511b60