feat(storage): expose send_and_append on OpenAppendableObject

[vsharonlynn]

Issue #5716 .

This PR follows PR #6489 .

[gemini-code-assist]

Code Review

This pull request introduces the ability to send an initial chunk of data when opening a bidirectional write stream for appendable objects. It adds a new send_and_append method to the OpenAppendableObject builder, updates the internal state machine (AppendObjectSpecState) and connector to handle and preserve the initial chunk (including CRC32C checksum calculation), and updates the transport layer to correctly initialize the write offset and running checksum. There are no review comments, and the implementation looks solid and well-tested.

[codecov]

Codecov Report

❌ Patch coverage is 79.63526% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.28%. Comparing base (c4c8d56) to head (9afe3d7).
⚠️ Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
src/storage/src/storage/transport.rs	0.00%	45 Missing ⚠️
src/storage/src/storage/stub.rs	0.00%	10 Missing ⚠️
src/storage/src/storage/bidi_write/transport.rs	95.69%	4 Missing ⚠️
src/storage/src/storage/open_appendable_object.rs	69.23%	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    #6490      +/-   ##
==========================================
- Coverage   96.34%   96.28%   -0.07%     
==========================================
  Files         295      295              
  Lines       83478    83745     +267     
==========================================
+ Hits        80429    80635     +206     
- Misses       3049     3110      +61     

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