log-converter: Some timezones not extracted correctly.

[gibber9809]

Bug

In the timestamp regex used by log-converter the regex for extracting the timestamp offset from UTC is non-optional, meaning that simple timezones like Z can not be extracted properly.

E.g. the regex won't accept a timestamp like 2026-01-01T11:12:13.145Z.

CLP version

0.8.0

Environment

Ubuntu jammy docker environment.

Reproduction steps

1. Invoke log-converter on a test log file containing timestamps like the one mentioned in the issue description
2. Observe that timestamps are not perfectly extracted in the resulting IR