chore: enforce HTTPS-only URL validation and stage logging

[kireetivar]

This PR Improves Aviator connection diagnostics by enforcing HTTPS endpoints and adding clearer stage-level logging.

Changes

• Enforce HTTPS-only Aviator URLs.
• Continue supporting scheme-less hosts by normalizing them to https://.
• Normalize uppercase HTTPS schemes to lowercase.
• Reject unsupported schemes such as http, ftp, and invalid scheme values with a dedicated exception.
• Add shared URL scheme detection for Aviator and proxy handling.
• Include URL scheme and provided URL details in endpoint failure evidence.
• Add diagnostic start and completion logging for endpoint, DNS, TCP, proxy, TLS, gRPC, and credential stages.
• Improve PASS, FAIL, WARN, and skipped-stage log messages.
• Include resolved DNS addresses and exception details in diagnostic logs where available.
• Preserve structured skip reasons in diagnostic results.
• Add and update regression tests for URL validation, diagnostic reporting, stage logging, and proxy handling.

Testing

• Added and updated focused unit tests for Aviator URL normalization and connection diagnostics.