feat: Support for Proceed()'ing to base implementation

[DrBarnabus]

Adds support for proceeding to the base implementation of a non-abstract method in a mimicked class.

Example usage:

var mimickedClass = new Mimic<AbstractClass>();

mimickedClass.Setup(m => m.NonAbstractMethod())
    .Proceed();

mimickedClass.Setup(m => m.NonAbstractMethod())
    .Callback(() => Console.WriteLine("Still hit's callbacks!"))
    .Proceed();

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 72.47%. Comparing base (26d73e9) to head (2e4b6ed).

Files	Patch %	Lines
src/Mimic/Proxy/InterfaceProxyBase.cs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #5      +/-   ##
==========================================
+ Coverage   72.26%   72.47%   +0.21%     
==========================================
  Files          60       61       +1     
  Lines        1972     1991      +19     
  Branches      341      343       +2     
==========================================
+ Hits         1425     1443      +18     
- Misses        481      482       +1     
  Partials       66       66              

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