[WIP] Microbatch parallelism

[MichelleArk]

Resolves #

Problem

Solution

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 or 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.

TODO:

• consider adapter opt-in
• model-level configuration for parallel vs serial execution mode
• get dbt build working with MicrobatchModelRunner
• keyboard interrupts
• look into auto-detecting 'this' usage

Refactors:

• make batch_callback simpler + thread safe
• unify serial + parallel while loops
• override init on MicrobatchModelRunner to accept batch_idx, batches, and relation_exists
• refactor 'handler' to 'handle_microbatch_runner' on RunTask

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 8 lines in your changes missing coverage. Please review.

Project coverage is 86.41%. Comparing base (35c0920) to head (62f93ab).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10958      +/-   ##
==========================================
- Coverage   89.06%   86.41%   -2.65%     
==========================================
  Files         183      183              
  Lines       23634    23704      +70     
==========================================
- Hits        21049    20484     -565     
- Misses       2585     3220     +635     

Flag	Coverage Δ
integration	86.41% <94.73%> (+0.03%)	⬆️
unit	?

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Components	Coverage Δ
Unit Tests	86.41% <94.73%> (-2.65%)	⬇️
Integration Tests	86.41% <94.73%> (+0.03%)	⬆️