Fix Azure Unicode metadata round trips (10.0.14)

[KSemenenko]

Azure uploads fail when logical metadata contains a Unicode filename such as матеріал.txt, because those values are emitted directly as HTTP headers. The provider now encodes metadata requiring transport conversion in one versioned ASCII envelope and restores the original dictionary across portable upload/download/listing, conditional object, multipart and container operations.

Native ASCII metadata remains interoperable. Reserved-key collisions and malformed envelopes are covered, while content bytes, exact retry comparison and ETag conditions retain their existing behavior. The canonical package patch version is 10.0.14.

Validation: the unchanged provider failed 3 of 4 initial real-Azurite cases. After repair, 39 focused provider tests passed; the required non-BrowserStress suite passed 498 tests with 3 existing skips (501 total), including all six final metadata cases. Canonical solution formatting passed and the Release solution build finished with zero warnings and errors.

[codecov]

Codecov Report

❌ Patch coverage is 83.67347% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.33%. Comparing base (de3193e) to head (78e93b4).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...anagedCode.Storage.Azure/AzureMetadataTransport.cs	78.37%	2 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #122      +/-   ##
==========================================
+ Coverage   50.14%   50.33%   +0.18%     
==========================================
  Files         163      164       +1     
  Lines        8076     8112      +36     
  Branches     1071     1082      +11     
==========================================
+ Hits         4050     4083      +33     
+ Misses       3563     3560       -3     
- Partials      463      469       +6     

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