Code quality improvements: style, performance, and documentation

[memburg]

Summary

Comprehensive code quality review of the GiavaScript codebase covering:

• Crystal code style (conventions, naming, formatting)
• Algorithm performance (data structures, allocations, caching)
• Documentation (completeness, accuracy, spelling)

Style Issues (10 items)

• switch_statement_parser.cr:50 — while true → loop do
• function_runtime.cr:3-4 — Remove duplicate FUNCTION_NAME_REGEX constant
• interpreter.cr:6 — Fix inconsistent spacing in constant alignment
• runtime_types.cr:42-146 — Break long type-object hash lines
• 3 files — Duplicated identifier_start?, identifier_continue?, skip_whitespace methods
• interpreter.cr:887-957 — Condense truthy?/strict_equals_values? guard clauses
• expression_evaluator.cr:618-639 — Duplicate truthy? from interpreter
• giavascript_cli.cr:30 — Break ternary into named variable
• function_runtime.cr:40-42 — Use .try(&.size) for function_parameter_count
• interpreter.cr:835-838 — Break long control-flow condition

Performance Issues (8 items)

• interpreter.cr:1029-1034 — Single-pass string escape instead of chained .gsub
• runtime_types.cr:920-925 — Schwartzian transform for Array.sort to avoid O(n log n) string conversions
• runtime_types.cr:927-976 — In-place array_splice to reduce allocations
• runtime_types.cr:984-996 — In-place array_unshift to avoid full array copy
• interpreter.cr:413-485 — Bail-early in split_assignment_statement when no = present
• interpreter.cr:879-882 — Cache FallbackRawStatement results
• runtime_types.cr:1017-1022 — Use String.build for value_to_s to reduce allocations
• expression_parser.cr:329 — Use Set for parameter duplicate detection

Documentation Issues (10+ items)

• README.md — Fix broken logo fallback src attribute
• README.md — Update examples list to match actual files
• reference/Language.md — Document arrow functions, comments, unary plus, semicolon-free statements, console.log, typeof semantics
• reference/Math.md — Add edge-case notes for Math.max()/Math.min()
• CONTRIBUTING.md — Improve awkward wording and add CI note
• src/giavascript_cli.cr — Fix .ls → .js in usage message
• Create CHANGELOG.md
• Create .github/PULL_REQUEST_TEMPLATE.md and issue templates

What this does NOT change

• No functionality changes
• No API changes
• No spec/test changes