chore: javadoc and tests for api, context

[toddbaert]

This PR contains no functional changes, it:

• adds specific test for API context
• cleans up general merging test by using spy
• adds missing javadocs on API

fixes: https://github.com/open-feature/java-sdk/issues/939

:warning: Please don't merge before https://github.com/open-feature/java-sdk/pull/934 so we can avoid some conflicts.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.27%. Comparing base (a0b1d25) to head (d406218).

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #942      +/-   ##
============================================
+ Coverage     95.04%   95.27%   +0.22%     
- Complexity      392      393       +1     
============================================
  Files            38       38              
  Lines           888      888              
  Branches         54       54              
============================================
+ Hits            844      846       +2     
+ Misses           24       23       -1     
+ Partials         20       19       -1     

Flag	Coverage Δ
unittests	95.27% <ø> (+0.22%)	:arrow_up:

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[Kavindu-Dodan]

@toddbaert I think this can be rebased an considered for 1.8.1 release :)

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud