mbproxy: strip historical phase/wave/plan references from source comments

Comments described the *history* of how the code arrived (phase numbers,
wave IDs, review IDs, dated TODOs) instead of what it does today. That
scaffolding rotted as the codebase evolved. Cleaned 60 source files +
.gitignore; behaviour unchanged (387/387 tests still pass).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mbproxy/tests/Mbproxy.Tests/Proxy/Cache/ResponseCacheMultiplexerTests.cs

@@ -465,7 +465,8 @@ public sealed class ResponseCacheMultiplexerTests
     public async Task UncachedReads_BehaveIdentically_ToPhase10()
     {
         // Regression guard: PerPlcContext with Cache = null must behave byte-identically
-        // to Phase 10 — every FC03 read produces a backend round-trip (coalescing aside).
+        // to the non-cached path — every FC03 read produces a backend round-trip
+        // (coalescing aside).
         int backendPort = PickFreePort();
         await using var backend = new StubBackend(backendPort);