refactor: replace juju errors with pkg errors

[zhangzhenghao]

Summary

• replace all github.com/juju/errors imports with github.com/pkg/errors
• migrate stack/context helpers and preserve errors.Is behavior with package-level sentinel errors where needed
• remove the direct github.com/juju/errors dependency and checksums

Verification

• go build -p 1 ./client ./master ./server ./worker
• go test -p 1 ./common/... ./config ./dataset ./logics ./model/... ./storage/...
• git diff --check
• confirmed no tracked source or module dependency still references github.com/juju/errors

A local go test -p 1 -timeout 30m ./... attempt could not link the large client.test binary because the execution environment returned disk quota exceeded; the affected library packages above pass and the remaining large-package coverage is delegated to CI.

[codecov]

Codecov Report

❌ Patch coverage is 20.08734% with 549 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.98%. Comparing base (3b55615) to head (27fb6ec).

Files with missing lines	Patch %	Lines
storage/data/sql.go	11.62%	114 Missing ⚠️
storage/vectors/milvus.go	0.00%	53 Missing ⚠️
storage/data/mongodb.go	26.53%	36 Missing ⚠️
master/tasks.go	10.25%	35 Missing ⚠️
storage/cache/sql.go	14.63%	35 Missing ⚠️
storage/cache/redis.go	15.62%	27 Missing ⚠️
storage/vectors/qdrant.go	17.85%	23 Missing ⚠️
model/ctr/fm.go	0.00%	20 Missing ⚠️
storage/vectors/xvec.go	16.66%	20 Missing ⚠️
config/config.go	0.00%	19 Missing ⚠️
... and 27 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1364      +/-   ##
==========================================
+ Coverage   71.97%   71.98%   +0.01%     
==========================================
  Files          94       94              
  Lines       18838    18838              
==========================================
+ Hits        13558    13560       +2     
  Misses       3846     3846              
+ Partials     1434     1432       -2     

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