Improve showing map

[Joonalai]

This PR improves qgis_show_map marker by:

• Ensuring that all layers are in shown with correct order and visibility even before test teardown
• Not running extra code in teardown if timeout is set to zero
• Resizing the qgis_parent to match the canvas size
• Moving the message box window to proper top left corner
• Opening QGIS parent window even though GUI is disabled. This allows the tests that require the opened parent window to succeed even though the window is not visibel to user.

Resolves #38

[codecov-commenter]

Codecov Report

Patch coverage: 82.60% and project coverage change: +1.00 :tada:

Comparison is base (d81a06d) 54.66% compared to head (2a10245) 55.67%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #40 +/- ## ========================================== + Coverage 54.66% 55.67% +1.00% ========================================== Files 7 7 Lines 472 485 +13 ========================================== + Hits 258 270 +12 - Misses 214 215 +1 ``` | Flag | Coverage Δ | | |---|---|---| | pytest | `55.67% <82.60%> (+1.00%)` | :arrow_up: | 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=GispoCoding#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://app.codecov.io/gh/GispoCoding/pytest-qgis/pull/40?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GispoCoding) | Coverage Δ | | |---|---|---| | [src/pytest\_qgis/pytest\_qgis.py](https://app.codecov.io/gh/GispoCoding/pytest-qgis/pull/40?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=GispoCoding#diff-c3JjL3B5dGVzdF9xZ2lzL3B5dGVzdF9xZ2lzLnB5) | `54.68% <82.60%> (+2.01%)` | :arrow_up: |

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