Rust: Settings type

[youyuanwu]

Description

Add safe wrapper for QUIC_SETTINGS ffi type.
Add setters for each setting entry using macro.
Changed Configuration new() to use new Settings type and removed the manual ffi type.

MISC:
Preview settings is removed/regressed because the auto generated bindings do not have preview apis yet.
Rust code files are accumulated in src dir. We should add a dedicated dir inside src to keep all rust code together. Will do it in a separate PR.

Testing

Added simple test to set settings using setters, and get the settings using ffi type to verify they match.

Documentation

NA

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.91%. Comparing base (7b2fbaf) to head (0821c07).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4839      +/-   ##
==========================================
- Coverage   87.43%   86.91%   -0.53%     
==========================================
  Files          56       56              
  Lines       17634    17634              
==========================================
- Hits        15419    15327      -92     
- Misses       2215     2307      +92     

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