Re-introduce a token invalidation mechanism

[codecov[bot]]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (3cb03fb) 86.87% compared to head (71b6e63) 86.65%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #158 +/- ## ========================================== - Coverage 86.87% 86.65% -0.23% ========================================== Files 14 16 +2 Lines 1829 1933 +104 ========================================== + Hits 1589 1675 +86 - Misses 240 258 +18 ``` | [Flag](https://app.codecov.io/gh/Smithay/calloop/pull/158/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/158/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | `85.74% <94.35%> (-0.20%)` | :arrow_down: | | [ubuntu-latest](https://app.codecov.io/gh/Smithay/calloop/pull/158/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | `86.21% <94.35%> (-0.21%)` | :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](https://app.codecov.io/gh/Smithay/calloop/pull/158?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay) | Coverage Δ | | |---|---|---| | [src/io.rs](https://app.codecov.io/gh/Smithay/calloop/pull/158?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL2lvLnJz) | `74.07% <100.00%> (+0.13%)` | :arrow_up: | | [src/list.rs](https://app.codecov.io/gh/Smithay/calloop/pull/158?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL2xpc3QucnM=) | `100.00% <100.00%> (ø)` | | | [src/sys.rs](https://app.codecov.io/gh/Smithay/calloop/pull/158?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL3N5cy5ycw==) | `92.18% <100.00%> (-6.31%)` | :arrow_down: | | [src/token.rs](https://app.codecov.io/gh/Smithay/calloop/pull/158?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL3Rva2VuLnJz) | `100.00% <100.00%> (ø)` | | | [src/loop\_logic.rs](https://app.codecov.io/gh/Smithay/calloop/pull/158?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Smithay#diff-c3JjL2xvb3BfbG9naWMucnM=) | `86.66% <83.60%> (-1.01%)` | :arrow_down: |

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