Improve indirection alias resolution and call collection reuse

[pixge]

Motivation

• Avoid repeated AST call collection and repeated alias chain resolution during indirection analysis to improve performance and testability.
• Separate pure logic for alias resolution and call collection to make behavior easier to unit-test.
• Ensure alias chains and class-method call resolution are handled consistently across call graph construction and per-unit analysis.

Description

• Add pure helpers resolve_alias, collect_calls, and collect_calls_by_unit and use them to build a call_map for reuse across analysis steps.
• Introduce an alias_cache to memoize alias resolution and update _collect_call_graph to accept call_map and alias_cache for cached lookups.
• Reuse the call_map when computing resolved calls per unit to avoid repeated CallCollector invocations.
• Expand tests in tests/test_analyzers.py to cover alias chains and class methods and adapt existing tests to the new helpers.

Testing

• Ran python -m pytest tests/test_analyzers.py to validate the analyzer helpers and behavior.
• The test run completed successfully with all tests passing (5 passed).

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Codex Task