add unit test for /arana/pkg/trace/...

[RayMario]

What this PR does:
add unit test for /arana/pkg/trace/...
github.com/arana-db/arana/pkg/trace coverage: 100.0% of statements
github.com/arana-db/arana/pkg/trace/jaeger coverage: 90.9% of statements

Which issue(s) this PR fixes:

Fixes #741

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: +0.24% 🎉

Comparison is base (b40e2af) 39.30% compared to head (7f79e16) 39.55%.
Report is 1 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #767      +/-   ##
==========================================
+ Coverage   39.30%   39.55%   +0.24%     
==========================================
  Files         259      263       +4     
  Lines       26477    26595     +118     
==========================================
+ Hits        10407    10519     +112     
- Misses      14939    14943       +4     
- Partials     1131     1133       +2     

see 4 files with indirect coverage changes

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