Implement compile-time witness resolution verification

[Copilot]

Adds a JavaC compiler plugin that verifies witness(Ty<T>) calls will succeed at compile time, catching resolution failures (not found, ambiguous) before runtime.

Implementation

• WitnessResolutionProcessor: JavaC Plugin that scans AST for TypeClasses.witness() calls, extracts type arguments, and runs WitnessResolution.resolve() at compile time
• Plugin registration: Added META-INF/services/com.sun.source.util.Plugin for automatic discovery
• Tests: Demonstrates valid/invalid resolution cases (processor cannot self-bootstrap, so tests document expected behavior)
• Documentation: ANNOTATION_PROCESSOR.md covers usage in external projects

Usage

Add to compiler configuration:

<plugin>
  <artifactId>maven-compiler-plugin</artifactId>
  <configuration>
    <compilerArgs>
      <arg>-Xplugin:WitnessResolutionChecker</arg>
    </compilerArgs>
  </configuration>
  <dependencies>
    <dependency>
      <groupId>com.garciat.typeclasses</groupId>
      <artifactId>java-type-classes</artifactId>
      <version>1.0-SNAPSHOT</version>
    </dependency>
  </dependencies>
</plugin>

Compilation will fail with clear diagnostics:

// Compile error: "Witness resolution will fail at runtime:
// No witness found for type: NoWitnessType"
TestShow<NoWitnessType> show = witness(new Ty<>() {});

Notes

Uses Plugin API (not standard annotation processing) to access method invocation AST. Reuses runtime resolution logic for consistency.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Implement annotation processor</issue_title>
<issue_description>We can try implementing an annotation processor that verifies, at compile time, that a call to <T> T witness(Ty<T> ty) will succeed in terms of witness constructor resolution, per our resolution rules as described in the README file and as implemented in the library code.

(Witness instantiation (calling the constructors) is a separate issue.)</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Implement annotation processor #14

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 72 lines in your changes missing coverage. Please review.
✅ Project coverage is 60.79%. Comparing base (09cfa6d) to head (96eaea6).

Files with missing lines	Patch %	Lines
...eclasses/processor/WitnessResolutionProcessor.java	0.00%	72 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #15      +/-   ##
============================================
- Coverage     68.04%   60.79%   -7.25%     
  Complexity      234      234              
============================================
  Files            49       50       +1     
  Lines           604      676      +72     
  Branches         46       59      +13     
============================================
  Hits            411      411              
- Misses          170      242      +72     
  Partials         23       23              

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