fix(engine): search among siblings when executing Call instruction

[zharinov]

Summary

• Fixed Call instruction to search among siblings like inline patterns do
• This preserves the "safe refactoring" promise: extracting a pattern to a named definition should not change matching behavior
• Added skip_policy to checkpoints to support Call retry with sibling advancement

Problem

When using a named definition like (Num) inside a parent pattern, it should search among siblings the same way an inline pattern like (number) would:

Num = (number) @n
Q = (program (expression_statement (array (Num) @num)))

Previously this would fail to match the first number in [1, 2, 3].

Test

Added regression_call_searches_among_siblings test case.