[TS] Support linear RegExp literals in test and match

[CaelmBleidd]

DateUtils cannot reach its date-math parser because every intrinsic RegExp literal currently stops execution. Add core runtime semantics for a bounded linear subset used by its actual pattern and simpler date-fns token checks. These operations are available with EMPTY and FROZEN model selections and either residual-call policy.

The supported grammar is UTF-16 literals, finite character classes/ranges, ASCII \d/\w, capturing/noncapturing groups, start/end anchors, greedy atom +, and one optional fixed trailing group. A repeated atom must have a disjoint following atom, so it cannot require backtracking; variable-width patterns require ^. Flags, alternation, lookaround, backreferences, unsupported quantifiers, coercion and custom exec remain explicit limitations. The syntax budget is 256 source code units / 64 atoms.

Build Bool/ITE terms directly. Each greedy run scans the existing backing bound once; fixed unanchored patterns use a leftmost-match ITE chain. There is no bound-squared start × repetition expansion or interpreted regex loop. Match captures reuse the existing range-copy operation, with a fresh mutable result array, undefined absent captures, and index/input/groups metadata. Without /m, $ requires the absolute end, including rejecting a final newline.

Small hooks retain intrinsic regex identity across forks and handle lastIndex/properties without relying on missing structural SDK declarations. A custom test method follows ordinary dispatch; a custom exec callback stops rather than being bypassed. No frontend, SDK, dependency pin or model-catalog changes are needed.

Validation: 16 focused tests passed (7 RegExp test groups and 9 existing runtime-limitation tests), zero skips. They include the real DateUtils pattern with symbolic success/failure/optional captures, all four model/fallback profiles, default backing bound 1000, UTF-16 surrogate units, final LF/CR/CRLF/U+2028/U+2029, leftmost matching, fresh arrays, overrides and unsupported boundaries. Every generated witness in the replay test passes the original source in Node. Restoring the previous literal-allocation limitation makes the DateUtils source regression fail at its unexpected-unsupported-path assertion. CI-style :usvm-ts:detektMain :usvm-ts:detektTest passed with zero new findings.

This is deliberately partial RegExp support. Complex date-fns parseISO/format expressions, flags and dynamically constructed patterns remain outside it. The full 200-class rerun will measure diagnostic applicability on the combined fixes; these focused checks do not claim full-cohort coverage or performance results.