SDSTOR-22816: reject duplicate create_pg while inflight

[Hooper9973]

A retry before create finishes returns RETRY_REQUEST and does not allocate a second repldev. Once the pg is in the map, a later duplicate with the same info returns success.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 81.81818% with 4 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (stable/v4.x@d9a17ca). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/lib/homestore_backend/hs_pg_manager.cpp	81.81%	2 Missing and 2 partials ⚠️
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Additional details and impacted files

@@              Coverage Diff               @@
##             stable/v4.x     #477   +/-   ##
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  Coverage               ?   53.72%           
==============================================
  Files                  ?       39           
  Lines                  ?     6905           
  Branches               ?      941           
==============================================
  Hits                   ?     3710           
  Misses                 ?     2793           
  Partials               ?      402           

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[Copilot]

🟡 Changes recommended

The new regression test can deadlock when a fatal assertion fails.

1 open finding

• Release blocked create before fatal assertions to prevent test hangs · New

What changed in this PR

Prevents concurrent duplicate PG creation from allocating multiple replication devices.

Changes:

• Tracks in-flight PG creations under the PG lock.
• Returns RETRY_REQUEST for concurrent duplicates and adds regression coverage.
• Bumps the package version to 4.3.6.

File	Description
hs_pg_tests.cpp	Tests duplicate creation during an in-flight request.
hs_pg_manager.cpp	Adds atomic admission and cleanup for PG creation.
hs_homeobject.hpp	Stores in-flight PG identifiers.
conanfile.py	Bumps package version.

🧠 Review effort: Balanced

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[xiaoxichen]

feel free to merge once Yawen gives her approval.
Please also communicate with CM team for this changes

[Besroy]

LGTM