Cached inference of all definitions in an unpacking (#13979)

## Summary

This PR adds a new salsa query and an ingredient to resolve all the
variables involved in an unpacking assignment like `(a, b) = (1, 2)` at
once. Previously, we'd recursively try to match the correct type for
each definition individually which will result in creating duplicate
diagnostics.

This PR still doesn't solve the duplicate diagnostics issue because that
requires a different solution like using salsa accumulator or
de-duplicating the diagnostics manually.

Related: #13773 

## Test Plan

Make sure that all unpack assignment test cases pass, there are no
panics in the corpus tests.

## Todo

- [x] Look at the performance regression

crates/red_knot_python_semantic/src/lib.rs

@@ -22,6 +22,7 @@ pub(crate) mod site_packages;
 mod stdlib;
 pub(crate) mod symbol;
 pub mod types;
+mod unpack;
 mod util;
 
 type FxOrderSet<V> = ordermap::set::OrderSet<V, BuildHasherDefault<FxHasher>>;