feat: TermWrapper.from static factory with intersection return type

[jeswr]

Adds an overloaded public static from(term, dataset, factory) factory to TermWrapper.

What it does

• from(term: string, dataset, factory) returns InstanceType<This> & NamedNode<string>
• from(term: T extends Term, dataset, factory) returns InstanceType<This> & T
• The implementation is simply return new this(term, dataset, factory) — identical runtime behaviour to the constructor, so subclasses get the factory for free (Child.from(...) returns Child & NamedNode).

Because the return type intersects the wrapper with the RDF/JS term type, instances created via from can be passed directly to factory.quad(...), dataset.match(...) and any other Term position without casts — the pain point both #61 and #74 set out to fix.

What it deliberately does not do

This is the minimal, fully non-breaking slice: no generic parameter on TermWrapper, no getter restructuring, no IRdfJsTerm removal, no changes to the #subjectPredicate mapper signatures. The constructor and all existing typed getters are untouched, so existing code compiles unchanged.

Relation to existing PRs

Supersedes the TermWrapper.from slice of #74 (its from overloads and README updates are adopted here verbatim) and the #from slice of #61. The remaining parts of those PRs (#in, class-level generics, getter/IRdfJsTerm restructuring, mapper signature changes) are intentionally left for follow-ups.

Testing

• New test/unit/term_wrapper_from.test.ts: runtime assertions (subclass instance creation, constructor equivalence for string and Term inputs, accessor/dataset/factory behaviour) plus compile-level assertions (result assignable to NamedNode/Quad_Subject; passed to DataFactory.quad and DatasetCore.match with no casts; Literal term type preserved).
• npm test: 132 tests, 0 fail (5 pre-existing skips); new code at 100% coverage.
• npx typedoc: 0 errors; the 6 warnings are all pre-existing on main.

Review timing: This draft was prepared with Claude; I (@jeswr) will personally review it before it progresses. I'm currently batching a lot of work in flight, so expect active review Wednesday-Friday (8-10 July).