fix: correct quote-fee accounting and expose net backtest profit

[grorge123]

Summary

This PR corrects quote-currency fee accounting and exposes net realized profit in BBGO backtest reports.

Changes

• Correct quote-currency fee handling in Position.AddTrade:
  • Buy trades add the fee to the quote cash cost.
  • Sell trades subtract the fee from quote proceeds.
  • Futures behavior remains unchanged.
• Fix TradeStats.TotalNetProfit so it consistently uses Profit.NetProfit.
• Add SummaryReport.TotalNetProfit and aggregate profit across all symbols.
• Preserve SummaryReport.TotalProfit for the existing PnL.Profit behavior.
• Update the backtest report UI to display both gross profit and net profit.
• Add regression tests for:
  • Quote-fee position accounting.
  • Net profit aggregation.
  • Partial closes and multiple quote-fee trades.
  • Profit fixer behavior.

Validation

• go test ./pkg/types and go test ./pkg/backtest/ — Passed.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

❌ Patch coverage is 81.25000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 22.13%. Comparing base (55c1586) to head (927ca2e).
⚠️ Report is 149 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/cmd/backtest.go	0.00%	2 Missing ⚠️
pkg/types/position.go	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2562      +/-   ##
==========================================
+ Coverage   20.89%   22.13%   +1.24%     
==========================================
  Files        1154     1168      +14     
  Lines       80239    81006     +767     
==========================================
+ Hits        16766    17934    +1168     
+ Misses      61944    61513     -431     
- Partials     1529     1559      +30     

Files with missing lines	Coverage Δ
pkg/backtest/report.go	0.00% <ø> (ø)
pkg/types/trade_stats.go	33.05% <100.00%> (+16.31%)	⬆️
pkg/types/position.go	38.51% <91.66%> (+0.76%)	⬆️
pkg/cmd/backtest.go	0.00% <0.00%> (ø)

... and 5 files with indirect coverage changes

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