fix: redirect input key in all file-system key-value store operations

[vdusek]

Only get_value mapped the logical input key (INPUT) to the actual input file on disk (e.g. INPUT.json). set_value, record_exists, delete_value, and get_public_url operated on the raw key, so set_value('INPUT', ...) wrote a second input file and reopening the store raised RuntimeError('Only one input file is allowed...'), breaking Actor.get_input() in local dev.

The input-key redirect is now extracted into a shared _resolve_input_key helper and applied to every key-addressing record method, so they all target the single input file consistently.

[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.94%. Comparing base (2cc5602) to head (e9a3d3c).
⚠️ Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
...ge_clients/_file_system/_key_value_store_client.py	93.75%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #976      +/-   ##
==========================================
+ Coverage   89.91%   89.94%   +0.02%     
==========================================
  Files          49       49              
  Lines        3085     3102      +17     
==========================================
+ Hits         2774     2790      +16     
- Misses        311      312       +1     

Flag	Coverage Δ
e2e	36.07% <62.50%> (+0.09%)	⬆️
integration	56.99% <81.25%> (+0.01%)	⬆️
unit	78.82% <93.75%> (+0.11%)	⬆️

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