Add some trace logging to the event loop

[codecov[bot]]

Codecov Report

Patch coverage: 47.05% and project coverage change: -0.31% :warning:

Comparison is base (b0f3b35) 87.15% compared to head (ab75b29) 86.85%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #152 +/- ## ========================================== - Coverage 87.15% 86.85% -0.31% ========================================== Files 14 14 Lines 1806 1818 +12 ========================================== + Hits 1574 1579 +5 - Misses 232 239 +7 ``` | [Flag](https://app.codecov.io/gh/Smithay/calloop/pull/152/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | Coverage Δ | | |---|---|---| | [macos-latest](https://app.codecov.io/gh/Smithay/calloop/pull/152/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | `85.90% <47.05%> (-0.33%)` | :arrow_down: | | [ubuntu-latest](https://app.codecov.io/gh/Smithay/calloop/pull/152/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | `86.39% <47.05%> (-0.31%)` | :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=Smithay#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files Changed](https://app.codecov.io/gh/Smithay/calloop/pull/152?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | Coverage Δ | | |---|---|---| | [src/sources/mod.rs](https://app.codecov.io/gh/Smithay/calloop/pull/152?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL3NvdXJjZXMvbW9kLnJz) | `94.21% <33.33%> (-0.98%)` | :arrow_down: | | [src/loop\_logic.rs](https://app.codecov.io/gh/Smithay/calloop/pull/152?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL2xvb3BfbG9naWMucnM=) | `87.53% <50.00%> (-1.16%)` | :arrow_down: |

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