test: add unit tests

[ZuLiangWang]

Which issue does this PR close?

Closes #

Rationale for this change

At present, the unit test coverage of CeresMeta is relatively low, many important modules and functions are not covered, there are hidden dangers, we need to improve the unit test.

What changes are included in this PR?

• Add unit tests for scheduler module.
• Add unit tests for procedure module.
• Add unit tests for meta module.
• Fix code coverage issues.

Are there any user-facing changes?

None.

How does this change test

Pass all unit tests.

[codecov[bot]]

Codecov Report

Merging #178 (5a3350b) into main (7f1354e) will increase coverage by 20.85%. The diff coverage is 56.67%.

@@             Coverage Diff             @@
##             main     #178       +/-   ##
===========================================
+ Coverage   39.66%   60.51%   +20.85%     
===========================================
  Files          34       40        +6     
  Lines        4213     4868      +655     
===========================================
+ Hits         1671     2946     +1275     
+ Misses       2317     1543      -774     
- Partials      225      379      +154     

Impacted Files	Coverage Δ
server/cluster/metadata/types.go	0.00% <0.00%> (ø)
server/coordinator/procedure/util.go	0.00% <ø> (ø)
server/storage/meta.go	0.00% <ø> (ø)
server/storage/storage_impl.go	57.21% <0.00%> (-5.10%)	:arrow_down:
server/cluster/manager.go	41.88% <34.88%> (ø)
server/coordinator/scheduler/scheduler_manager.go	53.96% <47.36%> (ø)
server/coordinator/procedure/manager_impl.go	73.68% <55.55%> (+73.68%)	:arrow_up:
server/coordinator/factory.go	79.61% <60.00%> (+75.15%)	:arrow_up:
server/cluster/metadata/cluster_metadata.go	54.10% <64.70%> (+54.10%)	:arrow_up:
server/id/id_impl.go	63.73% <75.00%> (ø)
... and 8 more

... and 6 files with indirect coverage changes