Expand AST node coverage and unify regex fallback for crypto detection

- Expand AST node types scanned per language:
  - C/C++: Add string_literal for algorithm names in function arguments
  - Java: Add string_literal for algorithm strings like "AES/GCM/NoPadding"
  - Go: Add selector_expression and identifier for package-qualified refs
  - PHP: Add string for cipher method names like 'aes-256-gcm'
  - Objective-C: Add message_expression for Obj-C method calls
  - Rust: Add path, path_expression, scoped_identifier, identifier

- Unify regex fallback behavior across all languages:
  - Replace separate Java/Swift/Objective-C fallbacks with unified approach
  - Only add algorithms not already found via AST detection
  - Reduces code duplication (~90 lines to ~35 lines)

- Add HKDF-SHA256 detection for Go std crypto library

- Update Go fixture to reflect more specific HKDF-SHA256 detection

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Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

Author: 3 people