Make extract_top_level_blocks() faster

[fredriv]

Resolves dbt-labs/dbt-core#9037

Description

This PR improves the performance of parsing docs files.
Duplicates the change from dbt-labs/dbt-core#9045 into dbt-common

Have verified the performance improvement in our local dbt project (~2300 models). Full parse time on my M1 Mac went from 2m20s to 41s.

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR
• I have run changie new to create a changelog entry

[fredriv]

Credit should really go to @peterallenwebb BTW for the original PR in dbt-core (dbt-labs/dbt-core#9045) which I've just re-created here 🙂

[fredriv]

Hi @dbeatty10! Do you know if there is a chance to get this merged into the next release of dbt-common? We're eager to get this fix into our systems to improve dbt performance 🙂

I just rebased my branch on the latest main branch so should be ready to merge I think. Let me know if there is anything else I need to do!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.48%. Comparing base (ed11c6c) to head (a45798c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #189      +/-   ##
==========================================
+ Coverage   68.33%   68.48%   +0.14%     
==========================================
  Files          52       52              
  Lines        3373     3389      +16     
==========================================
+ Hits         2305     2321      +16     
  Misses       1068     1068              

Flag	Coverage Δ
unit	68.48% <100.00%> (+0.14%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

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

[fredriv]

Updated my branch with latest changes in main now. Any chance of merging this PR @gshank @dbeatty10 @peterallenwebb? 🙏 Please let me know if there is anything more I should do 🙂

[gshank]

Closed in favor of #205