Add Uri.TryGetFileName() extension

[Copilot]

Adds a TryGetFileName() instance extension on Uri that extracts the file name from the last path segment, returning null when there is none.

Changes

• UriExtensions.cs — new TryGetFileName() method in the extension(Uri uri) block; uses direct segment indexing (no LINQ), URL-decodes the result via Uri.UnescapeDataString
• UriExtensionsTests.cs — covers file name extraction, percent-encoded names, and no-file-name cases

Example

new Uri("https://example.com/files/my%20file.pdf").TryGetFileName(); // "my file.pdf"
new Uri("https://example.com/files/report.csv?v=2").TryGetFileName(); // "report.csv"
new Uri("https://example.com/").TryGetFileName();                     // null

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.76%. Comparing base (6726493) to head (302eb08).
⚠️ Report is 5 commits behind head on prime.

Additional details and impacted files

@@            Coverage Diff             @@
##            prime      #77      +/-   ##
==========================================
- Coverage   93.99%   93.76%   -0.24%     
==========================================
  Files         132      132              
  Lines        2616     2678      +62     
  Branches      205      214       +9     
==========================================
+ Hits         2459     2511      +52     
- Misses        113      123      +10     
  Partials       44       44              

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