refactor: lib/slackMockをTypeScript化

[hakatashi]

Ref: #181

• lib/slackMockをTypeScriptに変換
• それに伴いTeamEventClientを使用している箇所の型注釈をEventEmitterに変換 (型が強くなっている (?) のでヨシ!)
• room-gatchaのテストが破滅したので大幅に書き直し

将来的にはSlackMock.webClientもProxyじゃなくてちゃんと全部jest.fn()でモックするようにしたい

[codecov[bot]]

Codecov Report

Patch coverage: 86.66% and project coverage change: -0.11% :warning:

Comparison is base (2cb8f74) 23.31% compared to head (d662415) 23.20%. Report is 3 commits behind head on master.

:exclamation: Current head d662415 differs from pull request most recent head 0a24db4. Consider uploading reports for the commit 0a24db4 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #845 +/- ## ========================================== - Coverage 23.31% 23.20% -0.11% ========================================== Files 173 173 Lines 15264 15292 +28 Branches 3489 3493 +4 ========================================== - Hits 3559 3549 -10 - Misses 10298 10336 +38 Partials 1407 1407 ``` | [Files Changed](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut) | Coverage Δ | | |---|---|---| | [amongyou/index.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-YW1vbmd5b3UvaW5kZXgudHM=) | `0.00% <ø> (ø)` | | | [atequiz/index.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-YXRlcXVpei9pbmRleC50cw==) | `79.56% <ø> (ø)` | | | [lib/slack.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-bGliL3NsYWNrLnRz) | `0.00% <ø> (ø)` | | | [lib/slackCache.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-bGliL3NsYWNrQ2FjaGUudHM=) | `83.83% <ø> (ø)` | | | [lib/slackUtils.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-bGliL3NsYWNrVXRpbHMudHM=) | `0.00% <ø> (ø)` | | | [map-guessr/index.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-bWFwLWd1ZXNzci9pbmRleC50cw==) | `0.00% <ø> (ø)` | | | [oogiri/index.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-b29naXJpL2luZGV4LnRz) | `0.00% <0.00%> (ø)` | | | [taimai/index.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-dGFpbWFpL2luZGV4LnRz) | `0.00% <ø> (ø)` | | | [lib/slackEventClient.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-bGliL3NsYWNrRXZlbnRDbGllbnQudHM=) | `83.33% <87.50%> (+3.33%)` | :arrow_up: | | [lib/slackMock.ts](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut#diff-bGliL3NsYWNrTW9jay50cw==) | `89.47% <89.47%> (ø)` | | | ... and [2 more](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut) | | ... and [4 files with indirect coverage changes](https://app.codecov.io/gh/tsg-ut/slackbot/pull/845/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tsg-ut)

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[smallkirby]

これ全然approveされてなくておもしろ

[hakatashi]

マージしちゃお