fix: leaks in flow and rate limit

[ankittk]

• When a flow failed or was cancelled,a background tasks is stuck forever waiting for data that would never come. This is Fixed by making sure all data pipes are properly closed when the flow ends.
• The rate limiter was busy-waiting and losing track of time between token refills.
• simple context loss

[codecov]

Codecov Report

❌ Patch coverage is 69.56522% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/calque/flow.go	71.42%	3 Missing and 1 partial ⚠️
pkg/middleware/ctrl/ratelimit.go	66.66%	1 Missing and 1 partial ⚠️
pkg/calque/handler.go	0.00%	1 Missing ⚠️

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[nullboundary]

@ankittk Awesome, nice bug catch!