perf(objects): add fastNullObject helper

[John-David Dalton (jdalton)]

Adds fastNullObject in src/objects/options.mts: shallow-copies own enumerable properties and sets the copy's prototype to null using the captured ObjectSetPrototypeOf primordial. The result keeps V8 fast properties, unlike a { __proto__: null, ...o } literal, which lands in dictionary mode. The input is never mutated.

getGlobMatcher now uses it for its options snapshot; a suppression on the call site records that the pollution guard lives inside the helper.

Verified with a V8 probe on Node 26.10: the null-proto literal reports dictionary elements, the helper result reports fast properties. Focused coverage is 100% statements/functions/lines (3 tests).

---

Note

Low Risk
Small additive utility with one internal consumer and focused tests; behavior change is limited to how options objects are copied for glob matching.

Overview
Introduces fastNullObject as a public @socketsecurity/lib/objects/options export: it shallow-copies optional input and sets the copy’s prototype to null via the captured ObjectSetPrototypeOf primordial, aiming to keep V8 fast properties instead of the dictionary-mode object that { __proto__: null, ...options } tends to create.

getGlobMatcher now normalizes its options argument with fastNullObject instead of an inline null-prototype spread; an oxlint suppression documents that the pollution guard lives in the helper.

Unit tests cover inherited keys, an own __proto__ property treated as data (not prototype mutation), and omitted options.

^{Reviewed by Cursor Bugbot for commit e821022. Configure here.}