Support explicit-port GitHub URLs

[turian]

Summary

• parse() returns incomplete metadata for GitHub URLs with explicit ports (e.g. https://github.com:8443/owner/repo.git) — the port causes domain mismatch, so the URL falls through to BasePlatform and loses owner/name extraction
• GitHub HTTPS, SSH, and git regex patterns now capture the port separately from the domain
• Added port_colon format helper in result.py for correct URL reconstruction (:8443 when port is set, empty otherwise)
• Ports are preserved across protocol rewrites (url2ssh, url2https, url2git)

Minimal reproduction

from giturlparse import parse

portless = parse("https://github.com/owner/repo.git")
with_port = parse("https://github.com:8443/owner/repo.git")

print("portless:", portless.valid, portless.owner, portless.name)
# portless: True owner repo

print("with_port:", with_port.valid, with_port.owner, with_port.name)
# Before fix: True  owner/repo.git   (falls through to BasePlatform)
# After fix:  True owner repo        (correctly parsed as GitHub)

Test plan

• All existing tests pass (no regressions)
• HTTPS with port: https://github.com:8443/Org/Repo.git → github, port=8443
• GIT with port: git://github.com:9418/Org/Repo.git → github, port=9418
• SSH URL-style with port: ssh://git@github.com:2222/Org/Repo.git → github, port=2222
• SCP-style without port unchanged: git@github.com:Org/Repo.git → github, port=""
• Blob/tree paths with port preserve path extraction
• Access token + port: https://user:token@github.com:8443/Org/Repo.git
• gist.github.com with port stays platform=github
• Malformed ports (github.com:abc) don't match GitHub
• Protocol rewrites preserve port across https↔ssh↔git
• Component rewrites (name, owner) preserve port

🤖 Generated with Claude Code

[protoroto]

@turian Hi, thanks for opening this pr! In order to make the CI pass may I ask you to:

• open an issue (if it's not already opened)
• add a changes/<number-of-issue-created>.feature file with a brief explaination of what's in this pr, so that when it will be merged and released this message will appear in the changelog
  Thanks again!