feat(optimizer): annotate types for ORDER BY alias references

[doripo]

When ORDER BY references a projection alias, annotate_types leaves the column typed as UNKNOWN:

import sqlglot
from sqlglot import exp
from sqlglot.optimizer import qualify, annotate_types

query = qualify.qualify(sqlglot.parse_one("SELECT x + 1 AS y FROM t ORDER BY y"), schema={"t": {"x": "INT"}})
annotated = annotate_types.annotate_types(query, schema={"t": {"x": "INT"}})
order = annotated.find(exp.Order)
print(order.expressions[0].this.type)  # UNKNOWN — should be INT

This happens because qualify_columns intentionally preserves ORDER BY alias refs (they're valid SQL in all dialects), so the annotator has no table-qualified column to resolve against.

This PR adds _resolve_order_by_alias, called from the column annotation path in _annotate_expression. When a bare column in ORDER BY matches a projection alias, it forces the projection's annotation via a recursive call if needed, then copies the type. Since qualify_columns has already added table qualifiers to projection columns, the recursive call resolves them via the normal path and does not re-enter the alias-ref code.

Test coverage includes basic alias resolution, shadowing/collisions, sort modifiers, compound expressions, set operations, window functions, subquery-as-projection, type coercion, and regression guards.

[doripo]

Happy to adjust the approach if you'd prefer this handled differently. A few notes on design choices:

• Post-pass vs. modifying _annotate_expression: I went with a post-pass to avoid touching the core annotation loop. The tradeoff is two walks over the ORDER BY subtree, but it keeps the change self-contained.
• _reannotate_subtree as a separate method: Seemed cleaner and potentially reusable for traversal-order gaps, but can be inlined into _fixup_order_by_aliases if preferred.

[georgesittas]

Why are we introducing a separate pass here? This method seems very costly. Is it possible to solve this more simply by resolving ORDER BY alias references to their projection expression types during the existing column annotation path (lines 390-425)?

[doripo]

Thanks for the quick review!

Switched to an in-loop approach in the new commit — _resolve_order_by_alias forces the projection's annotation via a recursive call when needed. Updated the PR description accordingly.

[doripo]

Note: _resolve_order_by_alias has extra logic to collect the last matching alias rather than returning on first match, to replicate behavior empirically observed on a local DuckDB and pinned as a test. On the other hand, duplicate alias resolution appears unspecified across dialects -- this could be simplified to an early return and the duplicate alias test dropped if preferred.