feat(tests): protocol dispatch test against canonical fixtures

[Taure]

Summary

Adds a per-SDK protocol dispatch unit test that feeds every canonical server-emitted message envelope through AsobiRealtime.HandleMessage and asserts the matching SDK event fires. Catches doc-vs-server drift (silent missed callbacks) before any user reports it.

The 32-fixture canonical corpus is vendored from asobi/priv/protocol/fixtures into Tests/Runtime/Resources/Fixtures/ and loaded at test time via Resources.LoadAll<TextAsset>.

Dispatch audit findings

Six dispatch cases were silently falling through to the generic OnMatchEvent / OnWorldEvent buckets, plus session.heartbeat had no surfaced event. Added explicit handlers and dedicated events:

Wire type	New event
match.finished	OnMatchFinished
match.matchmaker_expired	OnMatchmakerExpired
match.matchmaker_failed	OnMatchmakerFailed
world.finished	OnWorldFinished
world.list	OnWorldList
world.phase_changed	OnWorldPhaseChanged
session.heartbeat	OnHeartbeat

Decision: matchmaker.matched

Kept as a fall-through alias to OnMatchmakerMatched with a // TODO deprecate note (server only ever emits match.matched). Justification: someone got bitten by drift before and added it defensively; consumers may have wired up to it. Removing without a deprecation cycle is breaking. A dedicated test (MatchmakerMatchedAliasesMatchMatched) pins the alias so it is removed deliberately, not by accident.

Test design

• One [Test] per fixture via [TestCaseSource] (32/32 fixtures dispatched)
• One test per direction of the bijection: every fixture has an Expected mapping; every Expected entry has a fixture (catches stale entries on either side)
• One test pinning the matchmaker.matched alias

HandleMessage made internal and a parameterless test-only constructor added; visibility wired via Runtime/AssemblyInfo.cs -> [InternalsVisibleTo("Asobi.Tests")]. The test does NOT depend on MonoBehaviour and uses [Test] (not [UnityTest]), so it runs in EditMode-style isolation inside the existing PlayMode test asmdef.

CI status

CI will not pass on this PR until UNITY_LICENSE / UNITY_EMAIL / UNITY_PASSWORD secrets are added (#11). The dispatch test is correctly wired into the existing .github/workflows/smoke.yml workflow (it picks up everything under Tests/Runtime automatically, and testMode: playmode covers [Test] attributes in the runtime-test asmdef). It will run as soon as secrets are present.

Note: the pre-existing SmokeTest.cs has compile errors (it accesses .match_id / .players on string event payloads, calls SendMatchInput / Disconnect which do not exist) that predate this PR. They will surface once CI compiles tests; they are out of scope here per the "no SDK structural refactor" constraint and warrant a separate fix.

Test plan

• Add Unity license secrets (smoke CI: add UNITY_LICENSE / UNITY_EMAIL / UNITY_PASSWORD secrets #11)
• Verify DispatchTests.DispatchesFixtureToExpectedEvent parameterized cases all pass (32 cases)
• Verify EveryFixtureHasExpectedMapping and EveryExpectedHasFixture pass
• Verify MatchmakerMatchedAliasesMatchMatched passes

[Taure]

Heads up: #13 extracts the dispatch logic into a pure-C# AsobiDispatcher base class and runs the same 32-fixture suite from a standalone dotnet test project on stock ubuntu-24.04 (no Unity license needed). That makes #13's dispatch job the new required check for protocol regressions.

This PR (#12) stays useful — it documents the Unity-side intent and will run the PlayMode coverage as soon as the secrets in #11 are provisioned. Both can land in either order; git handles the duplicate commit cleanly when one rebases over the other.