Add consumer lock to events api

[adrianlyjak]

Add a consumer lock to the /events API handler to ensure reliable event consumption for a single connection, multiple connections are rejected until the first hangs up.

[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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[coveralls]

Pull Request Test Coverage Report for Build 18150157826

Details

• 35 of 37 (94.59%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.008%) to 90.236%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/workflows/server/server.py	35	37	94.59%

Totals
Change from base Build 18149922980:	-0.008%
Covered Lines:	1608
Relevant Lines:	1782

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💛 - Coveralls

[zhaotai]

Not sure in general if it's a good idea because there could be potential cases where users switch to different client or listen to same events from different clients.

Even though we want to limit only one session at the same time. We probably need to implement a mechanism to switch instead of reject.

But as a workaround, it's fine for now