chore: enforce the recommended linting rules for some files

[lenkan]

I thought we should make an effort to remove the relaxed linting rules. This is an initial effort to work towards enforcing the recommended linting rules for all files.

The changes to the lint config explicitly specifies the files that should have relaxed rules. The idea is that this list should eventually be removed once the entire codebase conforms to the rules.

In this PR I have only fixed some low hanging fruit in the test directory. If people think it is a good idea to enforce the rules I can do it for the rest. I would do it in my spare time so it might take a few weeks to do the overhaul.

In the long term, I think we will benefit greatly by getting rid of all the any types in the code base. Strict types will make it much easier to catch type errors and also improve the discoverability of the library.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.93%. Comparing base (1bc8a01) to head (3c459b1).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #279   +/-   ##
=======================================
  Coverage   83.93%   83.93%           
=======================================
  Files          48       48           
  Lines        4257     4257           
  Branches     1051     1025   -26     
=======================================
  Hits         3573     3573           
- Misses        656      680   +24     
+ Partials       28        4   -24     

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