Daily Test Coverage Improver: Add comprehensive API AST map tests (#7890)

* Add comprehensive tests for AST map API functions

Improved test coverage from 0% to 84% for src/api/api_ast_map.cpp by adding comprehensive tests for:
- Basic map operations (creation, insertion, lookup, size)
- Map manipulation (overwrite values, erase entries, reset)
- Reference counting (inc_ref/dec_ref)
- String representation (to_string function)

This contributes 94 newly covered lines to overall project test coverage.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* staged files

* Delete coverage-steps.log

* Delete coverage-summary.txt

* Delete coverage.html

* Delete z3.log

---------

Co-authored-by: Daily Test Coverage Improver <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/test/main.cpp

@@ -200,6 +200,7 @@ int main(int argc, char ** argv) {
     TST(egraph);
     TST(ex);
     TST(nlarith_util);
+    TST(api_ast_map);
     TST(api_bug);
     TST(arith_rewriter);
     TST(check_assumptions);