C frontends for codehelion.
Fast mode implements [codehelion_core::frontend::Frontend]: an
error-tolerant lexer paired with delimiter-matching unit-boundary
detection. Nothing here preprocesses or executes the source; directives
are dropped whole and macros pass through as ordinary tokens. Structural
mode lives in [ir]: a real tree-sitter parse mapped onto the
language-neutral Syntax IR.
Both modes share their machinery with the C++ frontend crate: the lexer is
parameterized by a [dialect::Dialect] carrying the keyword set, operator
inventory and dialect-only literal forms, and the structural CST walker is
parameterized by an [ir::IrMapping] carrying the node-mapping table.