feat: remote preflight, protocol version exposure, retry validation, …

[Anuoluwapo25]

…timestamp helpers

Implements four issues across the remote debugging and output subsystems:

closes #1254 – Remote: add preflight subcommand

• soroban-debug remote <addr> preflight [--output json|pretty] checks TCP connect, protocol handshake, auth, optional TLS, and an end-to-end ping without loading any contract.
• Both pretty and JSON output modes are supported; actionable suggestions are embedded in failure entries.

closes #1255 – Remote: expose selected protocol version in inspect output

• RemoteClient::selected_protocol_version() getter added.
• Protocol version is now printed in verbose remote output and in the remote inspect output when --verbose is active.
• doctor --remote now populates selected_protocol in its JSON report and prints it in the human-readable section.

closes #1257 – Remote: validate retry configuration before connecting

• --retry-attempts 0 is now rejected with a clear error and suggestion.
• --retry-max-delay-ms less than --retry-base-delay-ms is rejected with values and a correction hint.
• Help text documents the constraints and environment variable interaction.
• Man page updated automatically from the arg docstrings.

closes #1252 – Output: add stable timestamp formatting helpers

• format_timestamp_iso8601(SystemTime) -> String and now_iso8601() added to src/output.rs using the existing chrono dependency.
• Output is always UTC with a Z suffix; no locale dependency.
• Three unit tests cover the epoch, a known calendar date, and the structural format of the current-time helper.

Description

Related Issue

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update
• Refactor / code cleanup
• Performance improvement
• Test / CI improvement

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CI/Test Behavior Changes

What changed in CI or test behavior?

N/A — no CI/test behavior changes

Migration notes

N/A

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Checklist

• All tests pass locally (cargo test --workspace --all-features)
• Code is formatted (cargo fmt --all -- --check)
• Clippy is clean (cargo clippy --workspace --all-targets --all-features -- -D warnings)
• Commit message follows Conventional Commits
• PR description mentions the related issue(s)
• CI/test behavior changes documented above (or marked N/A)
• If CLI flags/subcommands/help text changed, man pages regenerated (make regen-man) and .1 files committed

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[Timi16]

FIx the conflicts

[Anuoluwapo25]

done @Timi16