feat(fixed_income): implement corporate bond pricing

[carlobortolan]

Closes #70.

Depends on #74.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 72 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.30%. Comparing base (fab7c7b) to head (c939d84).
⚠️ Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
src/fixed_income/bonds/corporate.rs	0.00%	72 Missing ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #77      +/-   ##
==========================================
- Coverage   92.64%   90.30%   -2.35%     
==========================================
  Files          29       30       +1     
  Lines        2775     2847      +72     
==========================================
  Hits         2571     2571              
- Misses        204      276      +72     

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