Avoid mutating caller components in FTP.build

[OskarEichler]

Summary

Normalize the FTP path after make_components_hash has copied the input. Do not replace entries in the caller Hash or Array before copying.

Reproduction

Build twice from {host: 'example.test', path: '/folder'}. Before, the first build changes the caller path to '/%2Ffolder' and the next build encodes it again. Frozen Hash/Array inputs raise FrozenError. After, repeated builds are equivalent and input components remain unchanged.

Verification

• Ruby 4.0.6 through rbenv; existing bundle exec rake test: 93 tests / 3,039 assertions / zero failures or errors, both baseline and this isolated patch.
• 72 checks cover Hash/Array and frozen/mutable containers, empty/relative/absolute paths and absent/a/i typecodes.
• Syntax and git diff --check pass. Supplemental Lint adds no findings against the 31-finding baseline.
• No test/spec files added or modified, per this contribution's explicit no-new-tests constraint. Focused reproductions ran externally.

Compatibility and limitations

Intentional ownership correction: FTP.build no longer mutates caller components. Generated URIs for the initial input remain the same. No public API removal, dependency change or Ruby minimum change.

Based on master 696df43b0be4c05d3a0dcf7db582126c915d860d. Other Ruby/OS runtimes were not executed locally. No production traffic or live mail/FTP services were used. Existing related PRs/issues were checked; this is a focused contribution, not exhaustive behavioral coverage.

[olleolleolle]

The change looks reasonable, and allows the caller to own what they passed in to the method.