feat(telegram): add telEgo backend

[Scratch-net]

Add telEgo as a selectable Telegram proxy backend.

This change:

• generates per-user UUID secrets for telEgo links;
• reads telEgo per-user traffic counters from the existing metrics endpoint;
• preserves Telemt accounting through the shared parser;
• handles integer, decimal, and scientific-notation Prometheus counter values.

A companion Hiddify Manager contribution installs telEgo v0.5.4 and generates its configuration: hiddify/Hiddify-Manager#5537.

The initial integration uses telEgo as an MTProxy backend only. Hiddify's current Telegram fake-domain setting is not an owned WEB hostname with a certificate, so exposing telEgo's WEB carriers requires a separate frontend and settings change. telEgo also does not support advertising tags.

Validation completed:

• Python compilation for all changed modules;
• Ruff check for the new metrics parser;
• focused Telemt and telEgo metrics parsing checks, including scientific notation;
• Jinja parsing and per-user link rendering checks.