fix: Fix checkGeneralCapacity slowly

[bigsheeper]

Cache the general count to speed up checkGeneralCapacity.

issue: #37630

[sre-ci-robot]

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[mergify]

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[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.07%. Comparing base (5e807c3) to head (328dd73).

Files with missing lines	Patch %	Lines
internal/rootcoord/meta_table.go	92.30%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #37976       +/-   ##
===========================================
+ Coverage   68.87%   81.07%   +12.20%     
===========================================
  Files         289     1360     +1071     
  Lines       25484   190842   +165358     
===========================================
+ Hits        17551   154728   +137177     
- Misses       7933    30623    +22690     
- Partials        0     5491     +5491     

Components	Coverage Δ
Client	72.33% <ø> (∅)
Core	68.87% <ø> (ø)
Go	83.24% <94.73%> (∅)

Files with missing lines	Coverage Δ
internal/rootcoord/constrant.go	100.00% <100.00%> (ø)
internal/rootcoord/create_collection_task.go	90.31% <100.00%> (ø)
internal/rootcoord/create_partition_task.go	91.39% <100.00%> (ø)
internal/rootcoord/meta_table.go	82.82% <92.30%> (ø)

... and 1067 files with indirect coverage changes

[bigsheeper]

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