feat: Expose getter and setter of aviatorEval for more customization

[HasonHuang]

• Expose getter and setter of aviatorEval for more customization.

For example, In concurrent processing scenarios, Enforcer uses ThreadLocal to manage multiple instances, but the AviatorEvaluatorInstance is a singleton, or custom configuration (enabling logging, performance optimization).

[casbin-bot]

@tangyang9464 @imp2002 please review

[codecov-commenter]

Codecov Report

Merging #359 (3842519) into master (3d22ec5) will increase coverage by 0.08%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #359      +/-   ##
==========================================
+ Coverage   69.37%   69.46%   +0.08%     
==========================================
  Files          49       49              
  Lines        2237     2240       +3     
  Branches      398      398              
==========================================
+ Hits         1552     1556       +4     
+ Misses        574      573       -1     
  Partials      111      111              

Files Changed	Coverage Δ
...ain/java/org/casbin/jcasbin/main/CoreEnforcer.java	77.62% <100.00%> (+0.57%)	:arrow_up:

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[github-actions[bot]]

:tada: This PR is included in version 1.40.0 :tada:

The release is available on:

• GitHub release
• v1.40.0

Your semantic-release bot :package::rocket: