Add acknowledgement progress support

[vvanglro]

Why

Long-running tasks can exceed a broker acknowledgement deadline while they are still processing successfully. Brokers that support progress acknowledgements need a generic way to expose that capability to task code.

Summary

• add an optional AckableMessage.ack_progress callback
• expose Context.ack_progress() and Context.is_ack_progressable
• route acknowledgement progress through the existing AckController
• allow repeated progress reports without marking the message as finally acknowledged
• make progress reports after final acknowledgement idempotent
• document broker integration and current broker support

Compatibility

Existing brokers do not need to provide the optional callback. Calling Context.ack_progress() for an unsupported message raises a clear RuntimeError. Currently, progress acknowledgement is implemented by the push- and pull-based JetStream brokers in taskiq-nats.

Related implementation

• Add JetStream acknowledgement progress taskiq-nats#27

Tests

• pytest -q — 294 passed
• ruff check .
• black --check .

[codecov]

Codecov Report

❌ Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.30%. Comparing base (9c339d6) to head (544d536).

Files with missing lines	Patch %	Lines
taskiq/context.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## master #640 +/- ##
==========================================
+ Coverage 80.20% 80.30% +0.09% 
==========================================
Files 69 69 Lines 2577 2595 +18 ==========================================
+ Hits 2067 2084 +17 - Misses 510 511 +1 

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