fix(targets): handle MySQL DSN scheme case

[overtrue]

Related Issues

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Summary of Changes

MySQL DSN parsing accepted only mysql:// and MYSQL:// prefixes. That left mixed-case schemes such as MySQL:// on the no-prefix path, causing the parser to treat the scheme as part of the username.

This PR makes MySQL scheme detection case-insensitive while preserving the original prefix spelling for redacted output. It also adds focused unit coverage for mixed-case parsing and redaction.

Verification

• cargo test -p rustfs-targets parse_dsn_with_mixed_case_mysql_prefix --lib
• cargo test -p rustfs-targets redact_dsn_with_mixed_case_mysql_prefix --lib
• cargo test -p rustfs-targets --lib
• cargo fmt --all --check
• git diff --check
• make pre-commit

Impact

Mixed-case MySQL DSN schemes now work consistently for target configuration and the recent MySQL connectivity probe. Existing lowercase, uppercase, and prefix-less DSNs keep the same behavior.

Additional Notes

N/A

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Pull request overview

This PR fixes MySQL DSN parsing/redaction in rustfs-targets by making mysql:// scheme detection case-insensitive, so mixed-case schemes like MySQL:// no longer fall through to the “no scheme” parsing path.

Changes:

• Replaced ad hoc strip_prefix("mysql://") / strip_prefix("MYSQL://") handling with a shared case-insensitive split_mysql_scheme() helper.
• Updated DSN parsing to strip any ASCII-case variant of mysql://.
• Updated DSN redaction to preserve the original scheme casing while still redacting passwords, and added unit tests for mixed-case parsing/redaction.