[ty] Suppress parenthesis completions for enum classes - #30441

Summary

Closes astral-sh/ty#3712.

With completions.completeFunctionParentheses enabled, accepting a class completion also inserts (). For enums that is almost never what the user wants: typing Color is nearly always a step towards Color.RED, and Color() both discards the member access and puts the cursor inside the parentheses.

Class completions for enum classes now skip the parentheses. This covers Enum, StrEnum, IntEnum, enum subclasses and subclasses of subclasses; non-enum classes are unchanged.

This follows the approach a maintainer suggested in the issue — @MichaReiser:

I don't think we should add a configuration option. Instead, we can suppress the completion for enums.

It also picks up #25832, which tried the same thing but was closed before merging.

Test Plan

New snapshot tests in crates/ty_ide/src/completion.rs cover Enum, an enum subclass, a subclass of a subclass, StrEnum and IntEnum, plus the existing complete_class_parentheses test for a plain class.

• cargo test -p ty_ide --lib
• cargo test -p ty_server --test e2e completions