feat: cache RestMethodInfo

[TimothyMakkison]

• Converted the string Name property to an expression that returns MethodInfo.Name
• Removed unused setters from properties
• AddProperties will reuse the same RestMethodInfo object instead of creating a new one for each request, saving 56 bytes per request.
  • Is this used by consumers or is it only for testing?
  • I could modify RestMethodInfo to contain a private pointer to the parent RestMethodInfoInternal and expose values as expression properties. This would save a couple of bytes for each use of RestMethodInfoInternal but would change the public constructor.

[codecov]

Codecov Report

Attention: Patch coverage is 95.83333% with 1 line in your changes missing coverage. Please review.

Project coverage is 84.90%. Comparing base (6ebeda5) to head (af19345).
Report is 160 commits behind head on main.

Files with missing lines	Patch %	Lines
Refit/RequestBuilderImplementation.cs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1903      +/-   ##
==========================================
- Coverage   87.73%   84.90%   -2.84%     
==========================================
  Files          33       36       +3     
  Lines        2348     2504     +156     
  Branches      294      363      +69     
==========================================
+ Hits         2060     2126      +66     
- Misses        208      299      +91     
+ Partials       80       79       -1     

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