When an identifier is used as an upvalue within a nested scope (e.g., a
`while` loop), the type checker needs to apply the global substitution
map to resolve `TypeVar`s that might have been determined in outer
scopes. This ensures that the correct type is used even if
`ctx.set_type` couldn't propagate the change directly through the
upvalue address.
This fix also includes a regression test to specifically cover this
scenario with series and closures.
Brummel
350b7b49b6