Add some type annotations

[peterallenwebb]

Description

Add some type annotations

Checklist

• [x] I have read the contributing guide and understand what's expected of me
• [x] I have signed the CLA
• [x] I have run this code in development and it appears to resolve the stated issue
• [x] I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• [x] I have run changie new to create a changelog entry

[codecov-commenter]

Codecov Report

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

Project coverage is 64.33%. Comparing base (db99ddd) to head (59c8a9e).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #156 +/- ## ========================================== + Coverage 64.31% 64.33% +0.02% ========================================== Files 51 51 Lines 3228 3230 +2 ========================================== + Hits 2076 2078 +2 Misses 1152 1152 ``` | [Flag](https://app.codecov.io/gh/dbt-labs/dbt-common/pull/156/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs) | Coverage Δ | | |---|---|---| | [unit](https://app.codecov.io/gh/dbt-labs/dbt-common/pull/156/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs) | `64.33% <100.00%> (+0.02%)` | :arrow_up: | 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=dbt-labs#carryforward-flags-in-the-pull-request-comment) to find out more.

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