fix: build null validity predicates without dynamic code generation

[ibgreen]

Goals

Allow Arrow builders to work in runtimes that prohibit eval and the Function constructor, without carrying a downstream bundle patch.

Closes #54.

Changes

• Replace dynamically compiled switch statements with captured validity predicates.
• Preserve the always-valid empty case and use direct comparisons for a single sentinel, including NaN.
• Use a snapshot Set for multiple sentinels, retaining primitive type distinctions and positive/negative-zero matching. Membership operates on supplied values directly rather than serializing them; object/symbol sentinels therefore use identity.
• Cover null, undefined, NaN, zeros, bigint, quoted/multiline strings, duplicates, input-list mutation and a blocked Function constructor.
• Remove the generated-source serializer and update the helper documentation.

Verification

• New predicate tests plus existing builder conformance: 447 passed.
• Final predicate rerun: 12 passed; changed-file ESLint passed.
• Source build type check: tsc --noEmit -p tsconfig/tsconfig.esnext.esm.json passed.
• Additional boundary checks passed with Node's --disallow-code-generation-from-strings flag.
• General root type-check commands report errors outside these changed files (ix resolution and existing bin/test/dependency typings); no compiler configuration is changed here.

The old switch-vs-Map performance claim is removed rather than retained for a different implementation. The single-sentinel fast path avoids Set lookup; multi-sentinel performance remains a review consideration. This does not claim to resolve any npm scanning hold.