Add and configure intersphinx

[dylanhmorris]

This PR

• Sets up cross referencing with other projects' documentation via intersphinx
• Improves cross referencing within the project
• Applies some minor wording changes, typo fixes, etc, partially addressing #245
• Closes #461

Not in this PR

• Not a full documentation formatting overview / typo fix, as there are some classes that may be simplified or removed, and there are some conventions to discuss (e.g. #464)

[codecov[bot]]

Codecov Report

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

Project coverage is 94.51%. Comparing base (907d1c1) to head (a56530c). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #463 +/- ## ========================================== + Coverage 94.41% 94.51% +0.09% ========================================== Files 42 42 Lines 1003 1003 ========================================== + Hits 947 948 +1 + Misses 56 55 -1 ``` | [Flag](https://app.codecov.io/gh/CDCgov/PyRenew/pull/463/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CDCgov) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/CDCgov/PyRenew/pull/463/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CDCgov) | `94.51% <100.00%> (+0.09%)` | :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=CDCgov#carryforward-flags-in-the-pull-request-comment) to find out more.

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