Fix linting warnings

[dlevy-msft-sql]

Summary

Fixes several linting warnings that have accumulated in the codebase.

Fixed Issues

File	Issue	Fix
\internal/io/file/file.go\	\io/ioutil\ deprecated since Go 1.19	Replaced with \os.ReadFile\
\internal/credman/credman_windows.go\	Redundant capacity in \make\	Simplified to \make([]*Credential, count)\
\internal/credman/credman_windows_test.go\	Unchecked errors	Explicitly ignored with _ =\

Remaining Warnings

The following warnings are not addressed in this PR as they involve complex unsafe pointer handling that requires careful review:

• 
  eflect.SliceHeader\ misuse in credman_windows.go (lines 76, 136)
• Unchecked \credFree.Call\ error in defer statement (line 75)

These should be addressed in a separate PR with proper testing.

Testing

• All tests pass
• Build succeeds

[Copilot]

Pull request overview

This PR resolves several Go linting warnings in the Windows credential manager and file I/O utilities without changing runtime behavior.

Changes:

• Replaced deprecated ioutil.ReadFile with os.ReadFile and cleaned up import ordering in the file I/O helper.
• Simplified make usage in EnumerateCredentials by removing redundant capacity specification and adjusted import ordering.
• Updated tests for the Windows credential manager to explicitly ignore setup/cleanup errors to satisfy linting while preserving original behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/io/file/file.go	Replaces deprecated ioutil.ReadFile with os.ReadFile and reorders imports to follow Go style.
internal/credman/credman_windows_test.go	Reorders imports and explicitly discards return values for WriteCredential/DeleteCredential where errors are intentionally ignored.
internal/credman/credman_windows.go	Reorders imports and simplifies slice allocation in EnumerateCredentials by removing unnecessary capacity argument.