Timezone handling

[ez-plugins]

Problem

Currently countdowns/announcements start relative to the server/process start time. For recurring announcements (for example, "announce every 2 hours") you must start the timer at the correct clock boundary and keep the process running. This is inconvenient and error-prone.

Use case

• I want the plugin to announce every 2 hours on the clock (e.g., 00:00, 02:00, 04:00...) regardless of when the server or bot was started.
• The schedule should be timezone-aware (e.g., align to the nearest timezone or a configured timezone per guild/server).

Proposed feature

Add an option for recurring timers to align to real-world clock intervals and to specify a timezone. Example configuration options:

• align_to_clock: boolean (default: false) - if true, align repeats to clock boundaries
• align_interval: string (e.g., "2h", "1d", or cron expression) - the interval to align to
• timezone: string (IANA timezone, e.g., "America/New_York") - the timezone to use for alignment; if omitted use server local or guild setting

Behavior examples

• interval: 2h, align_to_clock: true, timezone: "UTC"
  -> announcements at 00:00, 02:00, 04:00 UTC regardless of start time
• interval: 1d, align_to_clock: true, timezone: "Europe/London"
  -> announcements at 00:00 Europe/London each day

Acceptance criteria

• New option(s) available in configuration and/or command API to enable clock-aligned schedules and set timezone.
• Timers persist and re-calculate next run across process restarts.
• Handles DST changes correctly for named timezones.
• Backwards compatible: default behavior remains the current relative countdown.
• Documentation and examples added to README.

Implementation notes / suggestions

• Use a cron-like schedule parser or support both an interval+alignment flag and cron expressions.
• Use a timezone-aware library (e.g., luxon or moment-timezone) to compute next run times and handle DST.
• Persist schedule state so restart/resume works without manual intervention.