Fix panic in Python 3.12 line number handling

[sahinfalcon]

The read_varint function would panic when trying to read past the end of the line table. This fix adds bounds checking and returns Option to handle this case gracefully.

Changes:

1. Modified read_varint to return Option and added bounds checking
2. Modified read_signed_varint to handle the Option return type
3. Updated CompactCodeObjectImpl macro to handle Option return types with unwrap_or(0)

Fixes #735

[zanieb]

Nice! Do you know what the user-facing effect of this is? What happens when the delta is unwrapped to zero?

[sahinfalcon]

@zanieb It will assume that code is on the same line as the previous code and not crash with an index out of bounds error.

[benfred]

thanks for the fix!