Add a binding for Ctrl-Z to memray tree

[pablogsal]

CTRL+z to suspend isn't enabled by default, but we can add it with a keybinding.

Closes: #559

[godlygeek]

I've pushed a fixup here that gets this somewhere where I'm happy with it. Take a look, @pablogsal

[codecov-commenter]

Codecov Report

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

Project coverage is 92.94%. Comparing base (41248ed) to head (ef63b83). Report is 32 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #581 +/- ## ========================================== + Coverage 92.55% 92.94% +0.39% ========================================== Files 91 91 Lines 11304 11195 -109 Branches 1581 2047 +466 ========================================== - Hits 10462 10405 -57 + Misses 837 790 -47 + Partials 5 0 -5 ``` | [Flag](https://app.codecov.io/gh/bloomberg/memray/pull/581/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/581/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bloomberg) | `92.94% <ø> (+7.00%)` | :arrow_up: | | [python_and_cython](https://app.codecov.io/gh/bloomberg/memray/pull/581/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=bloomberg) | `92.94% <ø> (-2.78%)` | :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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