fix: general order executor: ClosePosition() works on futures position

[andycheng123]

No description provided.

[bbgokarma-bot]

Welcome back! @andycheng123, This pull request may get 215 BBG.

[c9s]

check e.position.IsShort() and avoid dust quantity?

[andycheng123]

For futures, the dust position still can be closed if the order is reduced only

[codecov]

Codecov Report

Merging #986 (5ad247c) into main (34866ce) will decrease coverage by 0.00%.
The diff coverage is 42.85%.

@@            Coverage Diff             @@
##             main     #986      +/-   ##
==========================================
- Coverage   19.91%   19.90%   -0.01%     
==========================================
  Files         420      420              
  Lines       31907    31922      +15     
==========================================
+ Hits         6353     6354       +1     
- Misses      24949    24962      +13     
- Partials      605      606       +1     

Impacted Files	Coverage Δ
pkg/bbgo/order_executor_general.go	17.10% <42.85%> (-0.55%)	⬇️

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[bbgokarma-bot]

Re-estimated karma: this pull request may get 252 BBG

[bbgokarma-bot]

Hi @andycheng123,

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