docs: refresh stale package documentation

[egillax]

Summary

• update stale R/Python setup guidance in README, installation guide, and Python helper docs
• remove stale KNN references and expand model-setting docs to include current model helpers
• fix stale vignette wording around splitting semantics, Andromeda storage, FeatureExtraction naming, and algorithm descriptions
• remove obsolete maintainer design vignette
• fix setPythonEnvironment() default envtype assignment to match documented behavior

Checks

• git diff --check
• Rscript -e 'files <- c("man/configurePython.Rd", "man/setPythonEnvironment.Rd", "man/runPlp.Rd", "man/createLearningCurve.Rd", "man/diagnosePlp.Rd", "man/createNormalizer.Rd", "man/iterativeImpute.Rd"); invisible(lapply(files, tools::checkRd))'
• R CMD build --no-build-vignettes .

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.90%. Comparing base (28e76aa) to head (29a6e2f).

Files with missing lines	Patch %	Lines
R/HelperFunctions.R	25.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #671      +/-   ##
===========================================
+ Coverage    89.89%   89.90%   +0.01%     
===========================================
  Files           49       49              
  Lines        13911    13911              
===========================================
+ Hits         12505    12507       +2     
+ Misses        1406     1404       -2     

☔ View full report in Codecov by Harness.
📢 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.