Add test to ensure multicall modules are loaded from compiled extensions

[BobTheBuidler]

Motivation

• Ensure the library is actually using compiled (mypy-compiled) extension modules when available instead of interpreted Python code.
• Prevent regressions where packaging or import paths fall back to pure-Python files even when ext_modules are built.
• Provide an automated assertion that key performance-sensitive modules are loaded as native extensions.

Description

• Add tests/test_compiled.py which defines test_compiled_extensions_loaded to validate compiled loading.
• The test imports multicall.call, multicall.constants, and multicall.multicall and inspects their __file__ paths.
• It asserts each module file suffix is one of the values in importlib.machinery.EXTENSION_SUFFIXES to ensure they are extension modules.

Testing

• No automated tests were executed as part of this change (tests were not run in the rollout).

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Codex Task