Add local presigned URL implementation for local clients

[pjbull]

Why

Using cloudpathlib.local as a drop-in test substitute currently fails when code calls as_url(presign=True), because local clients raise NotImplementedError. This breaks the documented local-testing workflow for code paths that generate presigned URLs.

What changed

LocalClient._generate_presigned_url now returns a deterministic local URL instead of raising. It reuses the local public URL and appends stable query parameters:

• expires=<expire_seconds>
• signature=local

This keeps behavior simple and predictable for tests while preserving the existing expire_seconds interface.

Tests

Added test_as_url_presign in tests/test_local.py to verify presigned URL generation for:

• LocalAzureBlobClient
• LocalGSClient
• LocalS3Client

The test checks that the file path is preserved and expected query parameters are present.

Closes #525

[github-actions]

🚀 Deployed on https://deploy-preview-572--gallant-agnesi-5f7bb3.netlify.app

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.1%. Comparing base (8fa0307) to head (d86746b).

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #572     +/-   ##
========================================
+ Coverage    94.0%   94.1%   +0.1%     
========================================
  Files          28      28             
  Lines        2226    2232      +6     
========================================
+ Hits         2094    2102      +8     
+ Misses        132     130      -2     

Files with missing lines	Coverage Δ
cloudpathlib/local/localclient.py	91.8% <100.0%> (+2.1%)	⬆️

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