fix(storage): Add start appendable condition for bypassing full object checksum

[v-pratap]

We are getting checksum mismatch error for few of the appendable uploads, this condition was missing. We need to add this condition since full object checksum is not available for fastbyte objects.

[gemini-code-assist]

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[codecov]

Codecov Report

❌ Patch coverage is 97.77778% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 92.95%. Comparing base (45fe5af) to head (9721480).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
...rage/internal/async/writer_connection_impl_test.cc	97.67%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #15786   +/-   ##
=======================================
  Coverage   92.94%   92.95%           
=======================================
  Files        2454     2454           
  Lines      226878   226922   +44     
=======================================
+ Hits       210879   210929   +50     
+ Misses      15999    15993    -6     

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[scotthart]

/gemini review

[gemini-code-assist]

Code Review

This pull request addresses a checksum mismatch error occurring during appendable uploads. The fix involves adding a condition to correctly identify appendable uploads when finalizing a write, ensuring that the full object checksum is bypassed as it's not available for these types of objects. The change is logical and directly addresses the described problem. I have one minor suggestion to improve code readability.

[bajajneha27]

LGTM! Can we please add a testcase too?