chore: update linting scope

[TerryHowe]

What this PR does / why we need it:

Add some additional lint checks.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.29%. Comparing base (0fbecc4) to head (c9a7e61).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1852   +/-   ##
=======================================
  Coverage   87.29%   87.29%           
=======================================
  Files         143      143           
  Lines        5535     5535           
=======================================
  Hits         4832     4832           
  Misses        417      417           
  Partials      286      286           

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[TerryHowe]

codecov/patch is not useful here

[shizhMSFT]

LGTM with suggestions

[Copilot]

Pull Request Overview

This PR introduces additional linting rules and configuration to improve code quality. The changes include setting up a comprehensive golangci-lint configuration file and applying various linting fixes throughout the codebase.

• Adds a comprehensive .golangci.yml configuration file with multiple linters enabled
• Fixes import grouping and organization across multiple files
• Updates test helper functions to include t.Helper() calls and simplifies temporary directory/file handling

Reviewed Changes

Copilot reviewed 11 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
.golangci.yml	New comprehensive linting configuration with multiple linters enabled
internal/testutils/fetcher.go	Adds blank line to separate import groups
internal/testutils/error_fetcher.go	Reorganizes imports with proper grouping
internal/io/tar_utils_test.go	Simplifies temp directory handling using t.TempDir()
cmd/oras/root/manifest/index/create_test.go	Adds t.Helper() calls to test helper functions
cmd/oras/root/cp_test.go	Replaces inline struct literal with variable assignment
cmd/oras/internal/option/packer_test.go	Adds t.Helper() call to test helper function
cmd/oras/internal/display/status/text_test.go	Adds t.Helper() call to test helper function
cmd/oras/internal/display/status/progress/status_test.go	Adds t.Helper() calls to test helper functions
cmd/oras/internal/display/status/console/console_test.go	Adds t.Helper() calls to test helper functions
cmd/oras/internal/display/metadata/descriptor/manifest_fetch.go	Reorganizes imports with proper grouping

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[Wwwsylvia]

LGTM

[FeynmanZhou]

Hi @TerryHowe, are we able to merge this PR? You may want to rebase it before merging. Thanks

[TerryHowe]

New problem was introduced, so I've had to update.