Fix golangci-lint errors in AWS SDK v2 migration

[Copilot]

The AWS SDK v2 migration introduced 14 linting violations across gocritic, gofmt, lll, revive, and unused checks.

Changes

Performance & Memory

• Use index iteration instead of value copy for []types.ObjectVersion (128 bytes per iteration)
• Pass aws.Config by pointer instead of value (696 bytes per call)

// Before: copies 128 bytes per iteration
for _, object := range versions {
    // ...
}

// After: uses pointer to existing element
for i := range versions {
    object := &versions[i]
    // ...
}

Interface Naming

• Rename S3API → API to avoid s3.S3API stuttering

Line Length

• Split long interface method signatures:

ListObjectVersions(
    ctx context.Context, params *s3.ListObjectVersionsInput, optFns ...func(*s3.Options),
) (*s3.ListObjectVersionsOutput, error)

Code Cleanup

• Remove 3 unused helper functions and their imports
• Replace empty if-block with warning log for unsupported CA cert files
• Apply gofmt formatting

Test Updates

• Migrate folder_delete_objects_test.go mock client to AWS SDK v2 API interface

Original prompt

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This section details on the original issue you should resolve

<issue_title>[FEATURE] dedicated test</issue_title>
<issue_description>### What feature would you like?

we need dedicated test for b1fbe51

Why is this feature useful?

No response</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [FEATURE] dedicated test #24

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