test(controller): add goleak test cases to detect goroutine leaks

[dongjiang1989]

Summary

• Add goleak verification to the controller package test suite via TestMain, ensuring goroutine leaks are detected across all controller tests
• Add goleak coverage to the MCP server reconciler tests
• Prevent silent goroutine leaks from accumulating in the reconciliation loop

Test plan

• go test ./go/core/internal/controller/... — goleak runs automatically on every test
• go test ./go/core/internal/controller/reconciler/... — reconciler goleak tests pass

[Copilot]

Pull request overview

Adds go.uber.org/goleak to the Go module and wires it into controller-related test suites via TestMain, aiming to detect goroutine leaks during tests (notably around reconciler behavior).

Changes:

• Add go.uber.org/goleak dependency.
• Enable goleak verification for controller package tests via a new TestMain.
• Enable goleak verification for reconciler package tests via TestMain in the MCP server reconciler test file.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
go/go.mod	Adds the go.uber.org/goleak dependency.
go/core/internal/controller/goleak_test.go	Adds package-level TestMain to run goleak verification for controller tests.
go/core/internal/controller/reconciler/mcp_server_reconciler_test.go	Adds goleak TestMain for reconciler package tests.

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[dongjiang1989]

cc @EItanya PTAL