Add root_nodes parameter to ExpertKnowledge

[MAVRICK-1]

• Added root_nodes parameter to ExpertKnowledge.init
• Implemented _add_root_nodes_forbidden_edges() to automatically convert root nodes to forbidden edges
• Updated apply_expert_knowledge() and limit_search_space() to process root nodes
• Added comprehensive documentation and examples
• Added test_root_nodes_single() and test_root_nodes_multiple() tests

Fixes https://github.com/pgmpy/pgmpy/issues/2407

[MAVRICK-1]

cc @ankurankan

[ankurankan]

@MAVRICK-1 Thanks for the PR. The tests seem to be failing, could you please have a look?

[MAVRICK-1]

Its minor issue solving it

[MAVRICK-1]

@ankurankan all test passed

[MAVRICK-1]

@ankurankan I will resolve everything in this PR, as well as the others, by the end of the week. My exams are currently going on.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 94.28571% with 2 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 94.93%. Comparing base (0159c4a) to head (c3a358a). :white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
pgmpy/estimators/ExpertKnowledge.py	87.50%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #2423      +/-   ##
==========================================
- Coverage   94.93%   94.93%   -0.01%     
==========================================
  Files         183      183              
  Lines       24911    24944      +33     
==========================================
+ Hits        23650    23681      +31     
- Misses       1261     1263       +2     

Files with missing lines	Coverage Δ
pgmpy/estimators/expert.py	82.52% <100.00%> (+0.17%)	:arrow_up:
pgmpy/tests/test_estimators/test_expert.py	94.59% <100.00%> (+0.97%)	:arrow_up:
pgmpy/estimators/ExpertKnowledge.py	87.80% <87.50%> (-0.26%)	:arrow_down: