Pass SCP URI connection settings through the SSH options hash

[OskarEichler]

Summary

Put URI-derived port/password defaults in the nested :ssh hash consumed by Net::SCP.download!, while preserving explicit SSH options and their precedence.

Reproduction and evidence

The existing adapter passes URI port/password at the outer SCP-options level, but the class download! method only forwards options.delete(:ssh) to Net::SSH.start. A captured call for scp://user:example@host:2222/file previously lacked these values in :ssh; it now includes them. Frozen options and nested hashes remain unchanged. Explicit ssh: {port: 3333, password: 'override'} still wins over URI defaults.

Compatibility / breaking changes

URI port/password values previously ignored by this adapter now take effect as defaults. Explicit nested SSH options retain precedence; an absent URI password does not clear a supplied password. Percent-decoding is proposed separately. No secrets or real authentication were used in verification.

Verification and limits

• This focused branch passes the existing upstream suite: 36 tests / 70 assertions, Ruby 4.0.6, net-ssh 7.3.3, test-unit 3.7.8 and Mocha 2.1.0; all Ruby commands used rbenv.
• The combined release-based consumer candidate passes the suite with frozen string literals enabled, 10 focused cases, 2,906 model assertions, 24 URI-component assertions and 19 local scp/URI assertions. Combined evidence includes other separately proposed fixes and existing upstream frozen-string corrections; it is not attributed to this patch alone.
• No repository tests added/modified under the consuming project's explicit no-new-tests policy. Reproductions/models ran externally. No deployed servers, SSH connections or production data were used.
• All seven runtime files parse with the Ruby 2.6 parser; actual older-Ruby/Windows/remote-server matrices were not run locally. No upstream lint config exists; targeted lint has the same eight pre-existing warnings, with no new warnings.
• Existing upstream PRs/issues and contribution guidance were checked. Maintainer CI results are pending; no CI pass is claimed.