Fix python bindings to correctly pass gap penalties to C code

[ryanbarouki]

This PR fixes a bug where custom gap penalties (gap_open, gap_extend, terminal_gap_extend) provided via the Python wrapper were effectively ignored by the core C implementation.

The Issues

1. The underlying C function aln_param_init (in lib/src/aln_param.c) expects positive values to override the default penalties. It specifically checks if (gpo >= 0.0) before applying the user-provided value. However, the current Python wrapper (python-kalign/kalign/__init__.py) enforces that these parameters must be negative or zero, raising a ValueError for positive inputs.

2. There appears to be a typo on line 85 of lib/src/aln_param.c where it checks if(gpe >= 0.0) and then assigns tgpe. I suspect this is a copy-paste typo and should check if(tgpe >= 0.0).

As a result:

Issue 1:

1. Users are forced to pass negative values (e.g., -10.0) to satisfy the Python validation.
2. These negative values are passed to the C core.
3. The C core sees a negative value, fails the >= 0.0 check, and ignores the input, silently falling back to the default penalties (e.g., 55).

Issue 2:

1. One issue would be tgpe would only be set if gpe was set to be >=0 which seems undesirable.

The Fix

This change updates the parameter validation in python-kalign/kalign/__init__.py to enforce positive values for custom penalties. This aligns the Python API with the C core's expectations, ensuring that user-specified penalties are correctly passed and applied during alignment.

The existing default behavior (passing None, which converts to -1.0 internally) remains unchanged and continues to correctly trigger the C core's default parameter logic.