Fixes degraded performance of content analysis

[mykola]

Context

• Fix content analysis slow down for longer texts with AI activated.

Summary

This PR can be summarized in the following changelog entry:

• Fixes an unreleased bug where the content analysis would perform worse when processing longer texts.

Relevant technical choices:

• The researcher.getResearch( "morphology" ) takes some time so it was extracted to higher level from getComplexWords because when we have more than 100 sentences in the post it dramatically slow down processing.

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Active Premium plugin from branch feature/fix-assessments and activate AI.
• Create text with many sentences (500+).
• Publish the post and refresh the page.
• Open Premium Analysis - Analysis results.
• Notice the time when Fix with AI buttons appears.
• It should take less than 10 seconds (without fix - it takes about 1 minute)

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Default Block/Gutenberg/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

• This should not impact any other places.

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• I have written documentation for this change. For example, comments in the Relevant technical choices, comments in the code, documentation on Confluence / shared Google Drive / Yoast developer portal, or other.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins that Yoast SEO provides integrations for.
• I have added unit tests to verify the code works as intended.
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• I have written this PR in accordance with my team's definition of done.
• I have checked that the base branch is correctly set.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label.
• I have added my hours to the WBSO document.

Fixes #1651

[coveralls]

Pull Request Test Coverage Report for Build cb038903d7db53f4d8c19481d65a0ac3993f8193

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall first build on 1651-ai-fix-content-analysis-slow-down at 57.304%

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Totals
Change from base Build 0ddbf26850e1b61d0a4698e71534609155527ecc:	57.3%
Covered Lines:	13313
Relevant Lines:	22777

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💛 - Coveralls

[mhkuu]

LGTM, nice find! 🎉

[mhkuu]

ACC: Works! 🎉