fix(connectrpc-build): suppress unused_qualifications + impl_trait_redundant_captures in generated mod.rs

[iainmcgin]

Adds unused_qualifications and impl_trait_redundant_captures to the #[allow(...)] block connectrpc-build writes into the generated mod.rs package tree, and documents the related refining_impl_trait_internal lint.

Why

The 0.4.0 codegen output trips two rustc lints in workspaces that build with -D warnings:

• impl_trait_redundant_captures: trait method RPITs carry a use<'a, Self> precise-capturing clause. It is required for edition-2021 consumers (RPIT-in-trait captures only 'static by default there) but redundant under edition 2024 (which captures all in-scope generics by default). Codegen targets both editions and cannot know the consumer's at write time, so the clause must stay — but it shouldn't warn.

• unused_qualifications: buffa 0.5 codegen always references sibling types through the canonical pkg::__buffa::view::* path even when a shorter natural-path re-export exists, because the re-export can be shadowed by a same-named proto type. The qualification is intentional. (Suppressed redundantly here on top of fix(buffa-codegen): add unused_qualifications to ALLOW_LINTS buffa#102 for connectrpc-build consumers whose protoc-gen-buffa toolchain hasn't picked up that release yet.)

Both lints fire at locations under the generated pub mod <pkg> tree that connectrpc_build::Config::include_file() writes, so the right scope for the suppression is the same #[allow(...)] block that already carries dead_code, unused_imports, etc.

refining_impl_trait_internal — known limitation, no codegen-side fix

This release also documents (CHANGELOG only) that refining_impl_trait_internal (warn by default since rust 1.86, rust-lang/rust#121718) fires on every handler impl, because the generated trait declares ServiceResult<impl Encodable<Out> + …> while the handler returns ServiceResult<Out>. The refinement is intentional — it lets handlers return either an owned message, a borrowed view, or MaybeBorrowed<M, V> — and is benign for handler impls. There is no place in the generated module tree where #[allow(...)] could reach the consumer's handler impl. Consumers who deny warnings should set refining_impl_trait_internal = "allow" in [lints.rust] (or workspace lints) or #[allow(refining_impl_trait)] on each handler impl block.

Verification

• cargo test -p connectrpc-build -p connectrpc-codegen --lib: 18 + 35 passed
• cargo build -p eliza-example -p multiservice-example: clean
• cargo clippy -p connectrpc-conformance -p eliza-example -- -D warnings: clean

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