Parser: report warnings for skipped invalid magic rules

[unclesp1d3r]

Summary

When loading magic files with invalid rules, the parser should report warnings about skipped rules instead of silently ignoring them.

Context

Per Core Flow 11 (Corrupted Magic File Handling), the parser should:

• Skip invalid individual rules and continue parsing
• Collect warnings about each skipped rule with line numbers
• Report summary: "Warning: Skipped N invalid rules in magic file"

Current state: Invalid rules are silently skipped. No warnings are collected or reported to the user.

Acceptance Criteria

• Parser collects warnings for each skipped rule (line number + reason)
• Warnings returned alongside successfully parsed rules (e.g., as a tuple or warnings field)
• CLI outputs warnings to stderr when rules are skipped
• Summary line: "Loaded N valid rules, skipped M invalid rules from {path}"
• Individual warnings include line number and error description
• Unit tests for warning collection
• Integration test with a magic file containing intentional errors

Files to Modify

• src/parser/mod.rs - Return warnings alongside parsed rules
• src/parser/grammar.rs - Collect parse failures as warnings
• src/main.rs - Display warnings to stderr
• src/lib.rs - Propagate warnings through library API

References

• Core Flows spec: Flow 11 (Corrupted Magic File Handling)
• Epic Epic: libmagic-rs Phase 1 MVP #24

[traycerai]

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