fast_api: require &'static for CFunction overload storage

[divybot]

Summary

Resolves #1989 by enforcing — at the Rust type level — the
storage-lifetime invariant introduced by upstream V8 change
crrev.com/c/7828135
([fastapi] Store v8::CFunction pointer directly in FunctionTemplateInfo,
slated for V8 15).

Before that V8 patch, FunctionTemplate::NewWithCFunctionOverloads copied
each v8::CFunction into a Managed<CFunctionWithSignature> heap object, so
the embedder's overload storage only needed to outlive the call. After it,
V8 retains the raw v8::CFunction* directly inside FunctionTemplateInfo
and reads it back on every fast-call dispatch, so the pointed-to storage
must outlive every FunctionTemplate that references it — which in
practice means 'static (templates can live until isolate disposal).

Today FunctionBuilder::build_fast accepts any &[CFunction] and forwards
as_ptr() to V8, so a deno_core-style call shape like
builder.build_fast(scope, &[fast_function]) would silently dangle once the
V8 15 ABI lands. This PR makes that misuse a compile error today instead
of a use-after-free tomorrow.

Changes

• FunctionBuilder::build_fast now takes overloads: &'static [CFunction].
• fast_api::CFunction::new now takes type_info: &'static CFunctionInfo,
  so the type_info_ pointer it caches cannot dangle either.
• fast_api::CFunctionInfo::new now takes arg_info: &'static [CTypeInfo],
  same reason — the constructed CFunctionInfo caches arg_info.as_ptr().
• Doc comments on all three explain the invariant and the canonical
  static-promoted const pattern.

Tests / call sites

The existing call sites in tests/test_api.rs and benches/function.rs
already use the canonical pattern —

const FAST_TEST: fast_api::CFunction = fast_api::CFunction::new(
    fast_fn as _,
    &fast_api::CFunctionInfo::new(/* ... */),
);
// ...
.build_fast(scope, &[FAST_TEST]);

— which Rust static-promotes to &'static [CFunction; 1], so no test
changes are required. cargo check --benches and cargo test --test test_ui both pass locally; the test-suite test_api/test_cppgc
binaries also compile through the relevant call sites (their only
remaining errors here are missing third_party/icu/common/icudtl.dat,
unrelated to this change).

A new trybuild compile_fail test
tests/compile_fail/build_fast_local_overloads.rs
demonstrates that a runtime-built Vec<CFunction> is now rejected with
E0597 — argument requires that 'overloads' is borrowed for 'static.

Context

• Source issue: fast_api: tighten FunctionTemplateBuilder::build_fast overload-list lifetime for V8 15.x #1989
• Slack thread: https://deno-company.slack.com/archives/C03P8NFAJTY/p1778742608051239
• Upstream V8: crrev.com/c/7828135
• Related Node.js FFI work that motivated the upstream change: ffi: add V8 fast-call path nodejs/node#63140
• Prior denoland/v8 investigation: docs: V8 14.9 fast-call snapshot serialization investigation v8#21

Closes denoland/divybot#160

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