Trim trailing frames in offline encode path

[artuskg]

Bug fix: offline encode() should trim from tail, not head

Problem

In offline encode():

• odd mel length trimmed with mel[:, 1:]
• non-divisible downsample remainder trimmed with x[remainder:]

Both drop leading frames.

Resolution

• Trim trailing frame for odd mel length: mel = mel[:, :-1]
• Trim trailing remainder before downsample reshape: x = x[:-remainder]

Why this helps

This preserves earliest alignment and avoids forward-shifting the encoded sequence relative to streaming/incremental behavior.

Regression test

• tests/test_bugfix_encode_trim_optional.py::test_encode_trims_trailing_frames_not_leading_frames

How to run

VOXMLX_ENABLE_MLX_RUNTIME_TESTS=1 python3 -m unittest -v tests.test_bugfix_encode_trim_optional