Implement define-macro special form

[mark-friedman]

Implemented the define-macro special form, providing Common Lisp-style unhygienic macros.

Changes:

1. Core Implementation:

   • Added analyzeDefineMacro to src/core/interpreter/analyzers/core_forms.js.
   • This function evaluates the transformer body in a fresh, isolated interpreter instance during analysis.
   • It registers a wrapper function in the macro registry that invokes the transformer closure with the macro arguments.
   • Added define-macro to SYNTAX_KEYWORDS and SPECIAL_FORMS in src/core/interpreter/library_registry.js.

2. Library Support:

   • Created src/core/scheme/define-macro.sld, exporting define-macro.
   • Updated repl.js and web/main.js to automatically import (scheme define-macro) into the initial environment.
   • Updated tests/run_scheme_tests_lib.js to load and import (scheme define-macro) for test files.

3. Testing:

   • Added tests/functional/test_defmacro.scm covering basic usage, return values, and explicit transformer syntax.
   • Added this test to tests/test_manifest.js.

Test Results:

• Node.js Test Suite: 2021 passed, 0 failed, 7 skipped.
• Verified manual REPL usage.

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PR created automatically by Jules for task 433352381041054241 started by @mark-friedman

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