* main: (248 commits)
  [ty] bump conformance suite commit (astral-sh#24848)
  [ty] Pass unmapped type variables to `SpecializationBuilder::build_with` (astral-sh#24809)
  [ty] Avoid bookkeeping for unannotated functions (astral-sh#24842)
  [ty] Optimize signature checking based on number of arguments (astral-sh#24674)
  [ty] Avoid eagerly inferring legacy generic context (astral-sh#24841)
  [ty] Skip decorator inference for undecorated functions (astral-sh#24839)
  [ty] solve unions against generic protocols (astral-sh#24837)
  [ty] Lazily allocate parameter type builders (astral-sh#24838)
  [ty] Lazily compute call argument fallbacks (astral-sh#24836)
  [ty] Avoid collecting type context callables (astral-sh#24835)
  Bump ecosystem-analyzer to e7576e6 (astral-sh#24834)
  [ty] Support basic narrowing with aliased conditional expressions (astral-sh#24302)
  [ty] Fix project and workspace selection (astral-sh#24824)
  [ty] Fix missing memory usage attributes (astral-sh#24823)
  Fix setting selection for multi folder workspace (astral-sh#24819)
  Improve diagnostics for implicit calls to a possibly unbound unary operator. (astral-sh#24816)
  [ty] Update review pool (astral-sh#24818)
  Bump 0.15.12 (astral-sh#24815)
  [ty] Complete support for more detailed diagnostics on possibly unbound errors from implicit dunder calls against unions. (astral-sh#24676)
  Implement `#ruff:file-ignore` file-level suppressions (astral-sh#23599)
  ...

* main: (44 commits)
  Update cargo-bins/cargo-binstall action to v1.18.1 (#24855)
  Update dependency ruff to v0.15.12 (#24857)
  Update taiki-e/install-action action to v2.75.18 (#24864)
  [ty] Model bool-op branch snapshots (#24458)
  [ty] Support `Unpack[TypedDict]` in `**kwargs` signatures (#24653)
  Update prek dependencies (#24858)
  Update Rust crate bitflags to v2.11.1 (#24859)
  Update Rust crate clap to v4.6.1 (#24860)
  Update Rust crate mimalloc to v0.1.49 (#24862)
  Update Rust crate uuid to v1.23.1 (#24863)
  Update Rust crate rayon to v1.12.0 (#24866)
  Update Rust crate libc to v0.2.185 (#24861)
  [ty] Reserve union element storage (#24849)
  [ty] bump conformance suite commit (#24848)
  [ty] Pass unmapped type variables to `SpecializationBuilder::build_with` (#24809)
  [ty] Avoid bookkeeping for unannotated functions (#24842)
  [ty] Optimize signature checking based on number of arguments (#24674)
  [ty] Avoid eagerly inferring legacy generic context (#24841)
  [ty] Skip decorator inference for undecorated functions (#24839)
  [ty] solve unions against generic protocols (#24837)
  ...

…-sh#24674)

## Summary

This PR adds a fast path to signature subtyping that checks positional
parameter count compatibility (along with a few other cases) before
doing expensive per-parameter type comparisons. In short, if the
signatures have a different number of positional arguments, they can't
match up.

Not much movement on CodSpeed, but the `more-itertools` improvement at
least seems to be real based on local benchmarking (17x faster or
something like that).