Improve Type Annotations Coverage

[peterallenwebb]

Description

Add more 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

[github-actions[bot]]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.29730% with 1 line in your changes missing coverage. Please review.

Project coverage is 64.30%. Comparing base (d25c29a) to head (43d47b3).

Files	Patch %	Lines
dbt_common/utils/casting.py	66.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #162 +/- ## ======================================= Coverage 64.30% 64.30% ======================================= Files 51 51 Lines 3202 3202 ======================================= Hits 2059 2059 Misses 1143 1143 ``` | [Flag](https://app.codecov.io/gh/dbt-labs/dbt-common/pull/162/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/162/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dbt-labs) | `64.30% <97.29%> (ø)` | | 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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