fix: Do not override the library user's AddMutationConventions() configuration

[rbeauchamp]

This pull request fixes issue #56, refactors various test classes, introduces new builder patterns for test scenarios, and updates documentation for clarity.

• README.md: Updated terminology and added a note on mutation conventions.
• GraphQLBuilderExtensions.cs: Renamed method AddReplicationServer to AddReplication.
• TestContext.cs: Ensured proper disposal of HttpClient.
• Test classes: Refactored to use TestContext property and TestScenarioBuilder.
• New files: Added TestScenarioBuilder.cs and TestScenarioOptions.cs for fluent test setup.

[linear]

ENG-2785 Do not override the library user's AddMutationConventions() configuration

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.50%. Comparing base (580b422) to head (7e19cee).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #57      +/-   ##
==========================================
- Coverage   99.51%   99.50%   -0.01%     
==========================================
  Files           7        7              
  Lines         205      204       -1     
  Branches       10       10              
==========================================
- Hits          204      203       -1     
  Partials        1        1              

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