Stabilize RPC subscription tests by fixing shutdown/httptest cleanup order

[Copilot]

TestFilteredSubscriptions could intermittently hang/timeout on Windows due to websocket lifecycle timing during test teardown. The issue was in test infrastructure cleanup ordering, not subscription filter logic.

• Root cause addressed: teardown ordering for WS-backed RPC tests

  • Updated wrapUnitTestChain cleanup registration so RPC shutdown runs before httptest.Server close during t.Cleanup execution (LIFO).
  • This avoids leaving websocket/hijacked connection handling in an unsafe shutdown sequence during subtest teardown.

• Change scope

  • Single-line behavioral change in test helper setup:
    • pkg/services/rpcsrv/server_helper_test.go

• Code change (illustrative)

  // before
  t.Cleanup(rpcServer.Shutdown)
  t.Cleanup(srv.Close)
  
  // after (LIFO => rpcServer.Shutdown runs first)
  t.Cleanup(srv.Close)
  t.Cleanup(rpcServer.Shutdown)

[AnnaShaleva]

Valid one, let's give it a try.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.49%. Comparing base (e5f1e3f) to head (cacc3b8).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4275      +/-   ##
==========================================
- Coverage   83.50%   83.49%   -0.01%     
==========================================
  Files         359      359              
  Lines       44168    44168              
==========================================
- Hits        36883    36879       -4     
- Misses       5467     5470       +3     
- Partials     1818     1819       +1     

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