compiler: port TypeChecker.res + TypeSuperposition.res -> .affine

Modules 5 + 6 (1123 + 323 lines), both verified green with affinescript check and
the full harness (all six modules ok).

TypeChecker.affine: the static checker. The .res's shared-mutable env (fresh-var
counter + substitution map) and checkResult.errors are unified into one immutable,
threaded CheckState, returned via (result, CheckState) tuples. The lexical
environment is a frame-stack [[(String, Binding)]] (head = innermost); the
substitution map is an Int-keyed assoc list. Unification is faithful arm-for-arm
including numeric widening and the Echo/EchoR rule: same-kind structural only,
Echo<_,_> deliberately NOT unifying with EchoR<_,_> (erasure is irreversible). The
Echo builtins (echo / echo_to_residue / residue_strictly_loses / echo_input /
echo_output) mirror the .res including the [Stab-Erase] diagnostics. Internal `ty`
constructors are C-prefixed (CInt..CVar) to avoid colliding with Types' TypeExpr.

TypeSuperposition.affine: the quantum-type demo (Collapsed | Superposition(...));
the deterministic collapse index is byte-faithful.

Documented faithful deviations: the .res `exprLoc` helper is omitted — `infer_expr`
returns the expression's own Location (a copyable summary) alongside the type, so
diagnostics keep exact locations without re-traversing a consumed node;
Array.zip/every/forEach over state-mutating callbacks become state-threading folds;
minor local renames to avoid global-constructor collisions. No type rule,
diagnostic, Echo/EchoR behaviour, or collapse arithmetic was changed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0195yA45jSSP7YDPwJSpw4bM

Author: hyperpolymath