chore: replace remaining `Result<T, Box<dyn Error>>`s with `anyhow::Result<T>` for consistency

[Iipin]

yeah

custom errors someday maybe

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@bc0fb75). Click here to learn what that means. Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #173 +/- ## ========================================= Coverage ? 28.05% ========================================= Files ? 18 Lines ? 1408 Branches ? 0 ========================================= Hits ? 395 Misses ? 1013 Partials ? 0 ``` | Flag | Coverage Δ | | |---|---|---| | rust | `28.05% <0.00%> (?)` | | 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=riichi#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://app.codecov.io/gh/riichi/chombot/pull/173?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=riichi) | Coverage Δ | | |---|---|---| | [src/slash\_commands/chombo.rs](https://app.codecov.io/gh/riichi/chombot/pull/173?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=riichi#diff-c3JjL3NsYXNoX2NvbW1hbmRzL2Nob21iby5ycw==) | `0.00% <0.00%> (ø)` | | | [src/slash\_commands/hand.rs](https://app.codecov.io/gh/riichi/chombot/pull/173?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=riichi#diff-c3JjL3NsYXNoX2NvbW1hbmRzL2hhbmQucnM=) | `0.00% <0.00%> (ø)` | | | [src/slash\_commands/mod.rs](https://app.codecov.io/gh/riichi/chombot/pull/173?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=riichi#diff-c3JjL3NsYXNoX2NvbW1hbmRzL21vZC5ycw==) | `0.00% <ø> (ø)` | | | [src/slash\_commands/pasta/command.rs](https://app.codecov.io/gh/riichi/chombot/pull/173?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=riichi#diff-c3JjL3NsYXNoX2NvbW1hbmRzL3Bhc3RhL2NvbW1hbmQucnM=) | `0.00% <0.00%> (ø)` | | | [src/slash\_commands/score.rs](https://app.codecov.io/gh/riichi/chombot/pull/173?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=riichi#diff-c3JjL3NsYXNoX2NvbW1hbmRzL3Njb3JlLnJz) | `0.00% <0.00%> (ø)` | |

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.