Fix replication metric emitter shutdown

[taylanisikdemir]

What changed?

MetricEmitterImpl was not waiting for underlying goroutine to finish before returning on Stop().

• Switched to ctx/cancel/waitgroup based implementation
• Used the same ctx in downstream calls so it doesn't stall on Stop
• Added new unit tests and verified no goroutine is leaking after stop.

Why?
Stops should not leave goroutines behind.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 71.03%. Comparing base (ce92cd8) to head (29e1c74).
Report is 1 commits behind head on master.

Additional details and impacted files

Files	Coverage Δ
service/history/replication/metrics_emitter.go	81.94% <83.33%> (+34.25%)	⬆️

... and 8 files with indirect coverage changes

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[coveralls]

Pull Request Test Coverage Report for Build 018feaa2-8fc3-4a42-84aa-10bd2ac726ee

Details

• 12 of 14 (85.71%) changed or added relevant lines in 1 file are covered.
• 34 unchanged lines in 11 files lost coverage.
• Overall coverage increased (+0.03%) to 70.885%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
service/history/replication/metrics_emitter.go	12	14	85.71%

Files with Coverage Reduction	New Missed Lines	%
common/types/shared.go	1	39.88%
common/cache/lru.go	2	93.01%
common/persistence/sql/sqlplugin/mysql/task.go	2	73.68%
service/history/replication/task_processor.go	2	82.76%
common/persistence/sql/sqlplugin/mysql/db.go	2	79.49%
common/persistence/historyManager.go	2	66.67%
service/history/handler/handler.go	3	96.2%
tools/cli/admin_db_decode_thrift.go	3	69.23%
common/persistence/statsComputer.go	3	98.21%
common/task/fifo_task_scheduler.go	5	82.47%

Totals
Change from base Build 018fea84-767f-4b7b-b478-9c0ffa321880:	0.03%
Covered Lines:	105592
Relevant Lines:	148963

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💛 - Coveralls