feat(storage): support initial payload in bidi_write transport

[vsharonlynn]

Issue #5716 .

[gemini-code-assist]

Code Review

This pull request introduces the ability to send an initial chunk of data when opening an appendable object in a bidirectional write stream, updating the connector, state, and transport layers to support and test this flow. The review feedback points out that the newly added public methods connect_open_and_append and new_open_and_append lack documentation, violating the repository style guide which requires all public items to be documented with ///.

[codecov]

Codecov Report

❌ Patch coverage is 96.93487% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.35%. Comparing base (c4c8d56) to head (711f73b).
⚠️ Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
src/storage/src/storage/bidi_write/transport.rs	95.69%	4 Missing ⚠️
src/storage/src/storage/bidi_write/connector.rs	96.93%	3 Missing ⚠️
src/storage/src/storage/bidi_write/state.rs	98.57%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #6489    +/-   ##
========================================
  Coverage   96.34%   96.35%            
========================================
  Files         295      295            
  Lines       83478    83677   +199     
========================================
+ Hits        80429    80626   +197     
- Misses       3049     3051     +2     

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