fix: bubble captures from named nodes without creating scope

[zharinov]

Summary

• Named nodes with internal captures now bubble fields up alongside the outer capture
• Previously, capturing a named node would incorrectly nest internal fields
• Added inner_creates_scope() to distinguish scope-creating expressions (sequences, alternations) from others

Example

Q = (function
  name: (identifier) @name :: string
  body: (block) @body
) @func :: FunctionInfo

Before: { func: { name: string, body: Node } } (nested)
After: { func: FunctionInfo, name: string, body: Node } (flat)

Test plan

• Added named_node_captured_with_internal_captures test