Update tests to support Textual 0.71

[godlygeek]

• Work around a Textual deadlock in our tests. There's a deadlock on shutdown when the pilot exits before the message pump has quiesced, but it doesn't occur when we wait for the message pump to become idle.
• Update our tests' Textual snapshots. The latest version of Textual uses a new SVG generation algorithm that results in some slight differences compared to the old algorithm's output, but should be more stable going forward. Additionally, the two trailing spaces removed by the previous commit show up as differences in these snapshots.
• Avoid extra trailing spaces on node in the tree reporter tree. If trailing spaces are included, they are highlighted with an orange background when the line is selected.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.00%. Comparing base (41248ed) to head (b30be4a). Report is 97 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #643 +/- ## ========================================== + Coverage 92.55% 93.00% +0.45% ========================================== Files 91 94 +3 Lines 11304 11415 +111 Branches 1581 2092 +511 ========================================== + Hits 10462 10617 +155 + Misses 837 798 -39 + Partials 5 0 -5 ``` | [Flag](https://app.codecov.io/gh/bloomberg/memray/pull/643/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bloomberg) | Coverage Δ | | |---|---|---| | [cpp](https://app.codecov.io/gh/bloomberg/memray/pull/643/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bloomberg) | `93.00% <100.00%> (+7.06%)` | :arrow_up: | | [python_and_cython](https://app.codecov.io/gh/bloomberg/memray/pull/643/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bloomberg) | `93.00% <100.00%> (-2.72%)` | :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=bloomberg#carryforward-flags-in-the-pull-request-comment) to find out more.

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[godlygeek]

Deadlock reported at https://github.com/Textualize/textual/issues/4699