the tria_io private subpackage had some unexpected error handling

[dkuegler]

• if IO failed, the functions just returned None instead of raising an exception (which would be best practice) --> changed this to raising IOError exceptions, so proper error handling is possible
• several messages meant for debugging were hard-coded, specifically the local verbose variables, best practice would be to handle this type of logging through the logging module

[codecov[bot]]

Codecov Report

Attention: 39 lines in your changes are missing coverage. Please review.

Comparison is base (98b6d7b) 35.01% compared to head (dccd831) 34.92%. Report is 6 commits behind head on main.

Files	Patch %	Lines
lapy/_tria_io.py	11.36%	39 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #50 +/- ## ========================================== - Coverage 35.01% 34.92% -0.09% ========================================== Files 14 14 Lines 2362 2365 +3 Branches 301 297 -4 ========================================== - Hits 827 826 -1 - Misses 1449 1455 +6 + Partials 86 84 -2 ``` | [Flag](https://app.codecov.io/gh/Deep-MI/LaPy/pull/50/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Deep-MI) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/Deep-MI/LaPy/pull/50/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Deep-MI) | `34.92% <11.36%> (-0.09%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Deep-MI#carryforward-flags-in-the-pull-request-comment) to find out more.

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