Header.OFFSET_X cannot be negative

[ceesb]

Bug: Header.OFFSET_X cannot be negative

Header.OFFSET_X is defined as an integer offset for the X axis, but writing a
negative value raises:

OverflowError: can't convert negative int to unsigned

Minimal Reproducer

import tempfile
import trsfile
from trsfile import Header, SampleCoding

path = tempfile.NamedTemporaryFile(suffix=".trs", delete=False).name

trs = trsfile.trs_open(
    path,
    "w",
    engine="TrsEngine",
    headers={
        Header.SAMPLE_CODING: SampleCoding.SHORT,
        Header.NUMBER_SAMPLES: 8,
        Header.SCALE_X: 4e-9,
        Header.OFFSET_X: -123,
    },
)

trs.close()

Expected Behavior

The file should be created successfully and OFFSET_X should round-trip as
-123.

Actual Behavior

OverflowError: can't convert negative int to unsigned

The exception comes from trsfile/engine/trs.py:

tag_value = b'\xff' * header.length if value is None else value.to_bytes(header.length, 'little')

int.to_bytes(..., signed=False) is the default, so negative integer headers
cannot be serialized.