Add expanded Ubuntu mirrors to mirror test list

[Copilot]

Expanded the mirror test set to include the requested Western European, nearby regional, and domestic Ubuntu mirrors, giving the tool a broader and more relevant pool for ranking. Mirror-facing docs were updated to reflect the new coverage and naming.

• Mirror test coverage

  • Added the new mirror URLs to test_mirrors() in xenonnet.sh
  • Kept the mirror/name arrays aligned so selection output remains consistent
  • Updated the section banner to a generic Ubuntu mirror analysis label

• Documentation sync

  • Refreshed the English and Persian README mirror lists
  • Updated mirror count/copy to match the expanded set

• Mirror naming

  • Corrected the ftp.calyx.nl entry label to match its hosting organization

Example:

Types: deb
URIs: http://mirror.netcologne.de/ubuntu/
Suites: noble noble-updates noble-backports
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg