fix: prevent hints from poisoning generic function inference in OR expressions

[Imran-S-heikh]

Summary

Fixes #1635.

This PR fixes a type inference bug where generic functions (like os.getenv) returned incorrectly widened types when used on the right-hand side of an or expression.

The Issue: When reassigning a variable like config: str | None, the type checker passed the variable's current type (str | None) as a "context hint" to the right-hand side of the or. Generic functions like os.getenv(key, default) accepted this hint, widening their return type to match the hint (inferring T as None) rather than inferring the specific type from their arguments (default="string" -> T=str).

This resulted in false positive type errors (e.g., Argument 'str | None' is not assignable...) even when a valid default value was provided.

The Fix

I updated boolop in expr.rs to adjust how hints are propagated in OR expressions:

• For Function Calls (Expr::Call): The context hint is now dropped. This forces the function to infer its return type strictly from its arguments (Inside-Out inference), preventing "poisoning" from the surrounding context.
• For Literals/Others: The context hint is preserved. This ensures that expressions like x: List[int] = None or [] still correctly infer List[int] instead of List[Any].

Test Plan

Added a regression test test_or_generic_function_hint_poisoning_fix in operators.rs.

The test simulates the os.getenv behavior using a generic identity function and verifies that:

1. A variable defined as str | None set to None.
2. Reassigned via variable or identity("default").
3. Correctly narrows to str (proving the hint str | None was ignored by the function inference).

Verification: Ran tests locally: cargo test -p pyrefly --lib test_or_generic_function_hint_poisoning_fix (Passed)

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