Deprecate Expr for functions that take only specific literals

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

This is the original comment that leads to this issue: https://github.com/apache/datafusion-python/pull/1484#discussion_r3079835791

**Describe the solution you'd like**

Add deprecation warnings, then remove`Expr` type hint in a later release

**Describe alternatives you've considered**

Leave as is

**Additional context**

We only allow specific values, so we can check them at the function invocation.

Start with the discussion linked from PR #1484 to identify which functions accept only specific literal values. Trace those function definitions and their type hints, then check how deprecation warnings are handled elsewhere. Done means the affected hints emit deprecation warnings and the intended later removal is documented or covered by tests.

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