fix: respect ignoreNulls flag in first_value and last_value

[andygrove]

Which issue does this PR close?

Closes #1630

Rationale for this change

What changes are included in this PR?

• Add tests
• Fix issue

How are these changes tested?

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.98%. Comparing base (f09f8af) to head (23a97cc).
Report is 131 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1626      +/-   ##
============================================
+ Coverage     56.12%   58.98%   +2.85%     
- Complexity      976     1066      +90     
============================================
  Files           119      125       +6     
  Lines         11743    12526     +783     
  Branches       2251     2339      +88     
============================================
+ Hits           6591     7388     +797     
+ Misses         4012     3973      -39     
- Partials       1140     1165      +25     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.