[ty] Fix hover to prefer expression nodes over identifiers
When hovering on an attribute name like 'value' in 'instance.value',
the minimal covering node is the Identifier, but we need the Attribute
expression to get the type. Update find_covering_node to track both
the minimal node and minimal expression, preferring the expression.
This fixes hover on attribute accesses. All hover tests now pass.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
