perf: memoize erb_nodes and tag_nodes in ProcessedSource

[ryanquanz]

Summary

Add memoized erb_nodes and tag_nodes methods to ProcessedSource so that multiple linters share a single AST traversal per file instead of each traversing independently. Update all linters to use the memoized methods.

Problem

Every linter that processes ERB or HTML tags calls ast.descendants(:erb) or parser.nodes_with_type(:tag) independently. With 15+ linters enabled, the same AST is traversed 10+ times per file.

Impact

The improvement is modest in isolation (~1–11% depending on workload), but compounds with other linter-level optimizations and eliminates redundant work across all linters.

Changes

15 files changed, +81 −23.

• Adds erb_nodes and tag_nodes memoized methods to ProcessedSource
• Updates 13 linters with mechanical s/ast.descendants(:erb)/erb_nodes/ replacements
• Private method signatures in RequireInputAutocomplete and RequireScriptNonce change from receiving parser to processed_source (internal only)
• 6 new tests in processed_source_spec.rb verifying memoization (object identity) and correctness (equivalence with non-memoized traversal)