Unit Testing: Support overriding macros in packages

[MichelleArk]

resolves #9624

Problem

It's not currently possible to override a macro that is referenced by its packaged-namespaced syntax. (e.g. dbt.current_timestamp, or my_package.my_macro). Only global references are overridden as expected.

Solution

Support overriding macros at the package-namespaced level, in addition to the global level (if it is a global macro) by:

• iterating over the provided overrides, and splitting them into global and package-namespaced macros
• apply package-namespaced overrides
  • if the package is dbt, also propagate the override to the global level
• apply global overrides
  • this ensures global overrides take precedence over package-namespacing if both override levels are provided (not sure why anyone would do this). confirmed with @graciegoheen that this is the desired behaviour
  • if the global override is a dbt macro, override it at the dbt package-level so that the dbt.my_macro reference is overriden as expected!

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.13%. Comparing base (d65bae5) to head (d51224b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9626      +/-   ##
==========================================
- Coverage   88.17%   88.13%   -0.04%     
==========================================
  Files         178      178              
  Lines       22460    22479      +19     
==========================================
+ Hits        19803    19811       +8     
- Misses       2657     2668      +11     

Flag	Coverage Δ
integration	85.51% <100.00%> (-0.12%)	⬇️
unit	62.54% <100.00%> (+0.18%)	⬆️

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