Support Conditional ternary operator

[zao111222333]

As #52, this PR supports Conditional ternary operator.
Those features have been implemented:

• BooleanExpression: Add field Cond(Box<BooleanExpression>, Box<BooleanExpression>, Box<BooleanExpression>). And update Display for BooleanExpression.
• parser: Implement parser for Cond, with priority: imp < cond < or.
• safe_eval_expression: Implement Cond's BDD with exsited function fn if_then_else(a: &Bdd, b: &Bdd, c: &Bdd) -> Bdd

There is one potential todo validation:

• Validation on BDD equivalence of A ? B : C and (A & B) | (!A & C)

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 90.06%. Comparing base (da57ff9) to head (cd9e9c1).

Files	Patch %	Lines
src/boolean_expression/_impl_boolean_expression.rs	42.85%	4 Missing ⚠️
src/boolean_expression/_impl_parser.rs	88.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #53      +/-   ##
==========================================
- Coverage   90.30%   90.06%   -0.24%     
==========================================
  Files          25       26       +1     
  Lines        1970     1993      +23     
==========================================
+ Hits         1779     1795      +16     
- Misses        191      198       +7     

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[daemontus]

I'll just merge this as-is and fix the clippy warning on main, so that you don't have to wait for me to re-run the workflow :) Otherwise it looks good, thank you!

[daemontus]

Released as 0.5.13.