feat(go): harden ergonomic wrapper and unbreak just go check

[kixelated]

Summary

The two-tier Go binding was already in place (raw moq-go-ffi + ergonomic moq-go wrapper), but just go check was red and the wrapper had a few rough edges. This unbreaks the build and hardens the wrapper. No wire/protocol or moq-ffi changes; this is wrapper + tooling only. Targets dev because the wrapper API changes are breaking (Session and Transport were bare FFI aliases).

Pre-existing build fixes (the check was already failing on dev)

These two masked each other: the stale test failed go vet before linking was ever reached, so the missing framework never surfaced.

• Stale test (moq_test.go) updated to the current PublishTrack / Consume / SubscribeMedia signatures (they gained info / subscription / maxLatencyMs params in an earlier refactor).
• Missing CoreServices framework (cgo.go): libmoq_ffi.a pulls in the notify crate's FSEvents backend, so any binary link (i.e. go test) failed with undefined _FSEventStream* symbols on darwin. Added -framework CoreServices.

Wrapper hardening

• Self-contained errors: all 19 FFI error variants re-exported as moq.Err* sentinels, plus IsAuthError, so consumers errors.Is without importing moq-go-ffi.
• Session wrapped as a real type with Closed(ctx) / Shutdown() / Cancel(code) instead of a bare FFI alias; Serve uses it rather than reaching into the raw type.
• Idempotent Close on Client and Server via sync.Once (Serve calls Server.Close on shutdown).
• Transport promoted to a defined type with TransportQUIC / TransportIroh / TransportWebSocket.
• Container constructors: LegacyContainer(), CmafContainer(init), LocContainer().
• Catalog() reports ErrClosed on an empty stream instead of (nil, nil).
• Cancellation semantics documented at the package level and in the README (the Used/Unused/Accept calls that have no native cancel).
• Added runnable godoc examples (example_test.go).

Testing

• check.sh now runs go test -race.
• Added concurrency tests covering the runCancellable concurrent-cancel-during-pending-call path and repeated/concurrent Cancel. Both pass under the race detector, validating the core async-to-sync bridge.

Test plan

• just go check passes (go vet, go build, go test -race)
• New race tests run under -race and pass (TestRecvGroupCancelRace, TestConsumerCancelConcurrent)
• gofmt -l clean

Public API changes (wrapper)

Breaking:

• Session is now a struct, not a type alias for ffi.MoqSession; its methods are Closed(ctx), Shutdown(), Cancel(code uint32).
• Transport is now a defined type (type Transport string) rather than an alias for string.

Additive:

• moq.Err* error sentinels (19), IsAuthError.
• TransportQUIC / TransportIroh / TransportWebSocket constants.
• LegacyContainer / CmafContainer / LocContainer constructors.

(Written by Claude)