gh-153486: Preserve negative indices in compact int subscript specializations

[KRRT7]

This follows up on gh-153486.

The base compact-int guard work tightened several specialized subscript paths to only stay specialized for non-negative compact integer indices. That kept the guards simple, but it also meant negative compact indices deoptimized even in cases where the specialized path could handle them correctly.

This PR restores negative-index handling in the specialized paths where it is valid and straightforward:

• BINARY_OP_SUBSCR_LIST_INT
• BINARY_OP_SUBSCR_TUPLE_INT
• BINARY_OP_SUBSCR_STR_INT
• BINARY_OP_SUBSCR_USTR_INT
• STORE_SUBSCR_LIST_INT

It does this by:

• keeping the specialization guards aligned with exact compact int indices
• normalizing negative indices inside the specialized path
• deopting only when the normalized index is still out of bounds

Tests are included to cover the negative-index specialized cases.