feat(rust): infer let types from Self-returning associated constructors

[zzet]

What

Extends the Rust extractor's local type environment: a let x = Type::new(..) already seeded x's type so a later x.method() selector call resolves against Type. This generalizes that seeding to the other conventional value constructors idiomatic Rust reserves for returning the owning type — from, default, with_capacity, with_config, empty — so let x = Matcher::from(cfg); x.find() binds find to Matcher::find.

Precision is preserved by two guards: (1) the inferred name must be a bare UpperCamelCase type, so a lowercase module function, Self, or a single-letter generic parameter is never seeded; (2) the resolver still refuses to bind unless that type genuinely owns the called method, so a misfit inference falls through to unresolved rather than to a wrong owner. Wrapper-returning constructors are deliberately excluded — from_str/open yield Result<Self> and builder a distinct struct, so their binding's real type is the wrapper, not the qualifier (admitting them was a latent wrong-owner risk this PR also removes).

Measured impact — honest

On ripgrep (native resolution, rust-analyzer off), this produces zero change in resolved-vs-unresolved edges: ripgrep's residual ambiguous method calls are dominated by common names (push/len/map/is_empty) on standard-library receiver types (Vec/String/Option/&[u8]) whose owner types aren't graph nodes, so no amount of native qualifier/receiver inference can bind them — that is inherently language-server territory. This change is a correctness/completeness improvement to the extractor (it infers more local types, and fixes the wrapper-constructor precision hole) that helps codebases with richer internal polymorphism than ripgrep; it is not expected to move recall on std-heavy repos.

Tests

• Extractor tests: Config::default() / Buf::with_capacity() / Matcher::from() seed the local type; thing::from (lowercase) and T::from (generic) do not.
• Resolver test: end-to-end bind of a constructor-bound local's method to the correct owner, refusing a same-named method on another type.
• go build, go test -race ./internal/parser/... ./internal/resolver/..., golangci-lint all green.