Diagnostic infrastructure for the CJC compiler.

This crate provides the core building blocks for reporting errors, warnings, and hints throughout the CJC compilation pipeline (lexer through MIR execution).

Key types

• Span — byte-offset range identifying a region in source code.
• SourceMap — precomputed line-start table for O(log n) byte-offset to (line, column) lookups.
• Diagnostic — a single error, warning, or hint with labels, hints, and optional fix suggestions.
• DiagnosticBag — growable collection of diagnostics with configurable error-count limits and batch rendering.
• DiagnosticBuilder — fluent builder for constructing diagnostics from typed ErrorCode values.
• DiagnosticRenderer — renders diagnostics to human-readable strings with source context, underlines, and optional ANSI color.
• ErrorCode — typed error code enum covering the entire compiler pipeline (E0xxx through E9xxx, W0xxx).
• Severity — error, warning, or hint classification.
• DiagnosticFormat — rich (multi-line with source context) or short (machine-readable one-liner) output format.