Rewriting the script and making it for Zabbix 7.0 LTS

[ableev]

Rewrite: split into modules, YAML config, Zabbix 7.0 support, tests

Modernizes the codebase after years of accumulated cruft.

• Splits the single 941-line zbxtg.py into a zbxtg_lib/ package (cli, directives, config, telegram_api, zabbix_web, zabbix_api, maps, utils). zbxtg.py/zbxtg_group.py remain as thin entry points at the same path — no changes needed to existing AlertScriptsPath setups beyond copying the new zbxtg_lib/ folder alongside them.
• Config moves to zbxtg_settings.yaml (see zbxtg_settings.example.yaml). Legacy zbxtg_settings.py is still auto-detected as a deprecated fallback.
• Graph fetching still scrapes the Zabbix web frontend (chart3.php) — verified against current Zabbix source that the JSON-RPC API still can't render images as of 7.0. Dropped the legacy Zabbix 2.x period= URL param (current frontend only accepts from/to); now targets Zabbix 4.0+, primarily 7.0. Added optional zabbix_api.py with Bearer-token support (6.4+) for future use.
• Fixed a latent bug: the location directive checked lat twice instead of lat and lon.
• Adds a pytest suite (47 tests) covering directives, config loading, both API clients, and an end-to-end CLI smoke test.
• README rewritten for the new layout, grammar cleaned up, screenshots unchanged.
• requirements.txt: added PyYAML, bumped requests/PySocks, dropped unused requests-oauthlib.