Timezone parsing accepts invalid values

## Issue Description

This is accepted as a valid timezone expression, and should not be: `+03:00.34`

Note that this is a regression, and this PR would fix it: https://github.com/arrow-py/arrow/pull/1165

## System Info

- 🖥 **OS name and version**: Ubuntu 25.10
- 🐍 **Python version**: Python 3.13.7
- 🏹 **Arrow version**: 1.4.0

Start by reproducing the reported timezone expression `+03:00.34` on Arrow 1.4.0, then inspect PR #1165, which the issue identifies as the regression fix. Done means the invalid expression is rejected and the behavior matches the intended correction in that pull request.

Written by the indexing model from the issue text.