fix: converter lose precision

[Yisaer]

goos: darwin
goarch: amd64
pkg: github.com/lf-edge/ekuiper/v2/internal/converter/json
cpu: Intel(R) Core(TM) i7-7567U CPU @ 3.50GHz
BenchmarkFloatParse
BenchmarkFloatParse-4 1000000 1044 ns/op
PASS

goos: darwin
goarch: amd64
pkg: github.com/lf-edge/ekuiper/v2/internal/converter/json
cpu: Intel(R) Core(TM) i7-7567U CPU @ 3.50GHz
BenchmarkIntParse
BenchmarkIntParse-4 1763830 661.6 ns/op
PASS

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 71.36%. Comparing base (1ebc3ae) to head (f31e9ec).
Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/converter/json/converter.go	73.91%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3445      +/-   ##
==========================================
+ Coverage   71.34%   71.36%   +0.02%     
==========================================
  Files         412      412              
  Lines       47154    47292     +138     
==========================================
+ Hits        33640    33748     +108     
- Misses      10886    10910      +24     
- Partials     2628     2634       +6     

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[ngjaying]

This is just