feat: Add overloads for CloudPath.open()

[0xbe7a]

Closes #465

To correctly handle the different argument and return types, I adapted the typeshed overloads for pathlib.Path.open() to CloudPath.open(). These overloads are appropriate because cloudpathlib passes the arguments to self._local after caching the file to local disk.

Handling all possible mode values is verbose, but the overloads are copied directly from typeshed, ensuring correctness and minimizing maintenance burden.

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Contributor checklist:

• I have read and understood CONTRIBUTING.md
• Confirmed an issue exists for the PR, and the text Closes #issue appears in the PR summary (e.g., Closes #123).
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[pjbull]

Thanks! A few changes requested. If you update soon, happy to include this in the next release coming in the next few days.

[codecov]

Codecov Report

Attention: Patch coverage is 94.11765% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.2%. Comparing base (5656879) to head (7daee5c).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
cloudpathlib/cloudpath.py	94.1%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #464     +/-   ##
========================================
- Coverage    94.2%   93.2%   -1.0%     
========================================
  Files          23      23             
  Lines        1728    1745     +17     
========================================
- Hits         1629    1628      -1     
- Misses         99     117     +18     

Files with missing lines	Coverage Δ
cloudpathlib/cloudpath.py	94.5% <94.1%> (-0.1%)	⬇️

... and 3 files with indirect coverage changes

[pjbull]

Thanks @0xbe7a!