Add fee_details to fee calculation

[tao-stones]

Problem

To reward priority fee differently from transaction fee (solana-foundation/solana-improvement-documents#96), priority fee and transaction fee should be separately identified from result of calculate_fee(...)

Summary of Changes

• define struct FeeDetails {}
• add new public api to calculate_fee_details(...) -> FeeDetails
• updated original calculate_fee(...) -> u64 without changing its logic to minimize impact on call sites
• feature gate to remove rounding

Feature Gate Issue: #34982

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 81.6%. Comparing base (531793b) to head (27e15a4).
Report is 6 commits behind head on master.

❗ Current head 27e15a4 differs from pull request most recent head fbd3e82. Consider uploading reports for the commit fbd3e82 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #35021   +/-   ##
=======================================
  Coverage    81.6%    81.6%           
=======================================
  Files         834      830    -4     
  Lines      224803   224838   +35     
=======================================
+ Hits       183467   183504   +37     
+ Misses      41336    41334    -2     

[apfitzge]

lgtm - thanks for introducing the feature for removing the rounding!