FEAT: Add option to use num of core for doc build

[dipinknair]

Tested in embedding examples repo https://github.com/ansys/pymechanical-embedding-examples/actions/runs/16144271451/job/45558949601?pr=266

Note: Doc build will take more time with this change

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ -0.02% (target: -1.00%)	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (3009349)	2544	2194	86.24%
Head commit (182b38e)	2548 (+4)	2197 (+3)	86.22% (-0.02%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#1230)	4	4	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

See your quality gate settings    Change summary preferences

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.22%. Comparing base (3009349) to head (182b38e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1230      +/-   ##
==========================================
- Coverage   86.24%   86.22%   -0.02%     
==========================================
  Files          39       39              
  Lines        2544     2548       +4     
==========================================
+ Hits         2194     2197       +3     
- Misses        350      351       +1     

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.