bbgo: add price check and add max leverage for cross margin

[c9s]

fix account value calculation

[codecov]

Codecov Report

Merging #935 (20dd37c) into main (cacc24f) will increase coverage by 0.01%.
The diff coverage is 26.19%.

@@            Coverage Diff             @@
##             main     #935      +/-   ##
==========================================
+ Coverage   20.01%   20.02%   +0.01%     
==========================================
  Files         410      410              
  Lines       30636    30705      +69     
==========================================
+ Hits         6131     6150      +19     
- Misses      23916    23966      +50     
  Partials      589      589              

Impacted Files	Coverage Δ
pkg/bbgo/risk.go	33.33% <26.19%> (-0.86%)	⬇️
pkg/strategy/bollmaker/dynamic_spread.go	0.00% <0.00%> (ø)

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