Emit an event right before the event dispatch loop starts

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[Copilot]

Pull request overview

Adds a new “loop started” hook to Basana’s dispatchers so consumers can run async initialization logic exactly once right before the dispatcher begins its dispatch loop (useful for pre-loop setup that must happen after run() begins, but before any events are processed).

Changes:

• Introduces subscribe_event_loop_started() on EventDispatcher and notifies registered handlers at the start of the dispatch loop.
• Wires the notification into both RealtimeDispatcher and BacktestingDispatcher dispatch loops.
• Adds/updates tests and documentation (CHANGELOG + repo Copilot instructions) to cover and describe the new behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
basana/core/dispatcher/base.py	Adds loop-started handler type, subscription API, and notification helper.
basana/core/dispatcher/realtime.py	Calls the loop-start notification before entering the realtime dispatch loop.
basana/core/dispatcher/backtesting.py	Sets initial backtesting “now” (from next event) and calls the loop-start notification before processing.
basana/core/dispatcher/__init__.py	Exports LoopStartedHandler in the dispatcher package API surface.
tests/test_realtime_dispatcher.py	Adds coverage ensuring realtime loop-start handlers are invoked once.
tests/test_backtesting_dispatcher.py	Adds coverage for backtesting loop-start invocation and duplicate subscription behavior.
CHANGELOG.md	Documents the new subscribe_event_loop_started feature.
.github/copilot-instructions.md	Updates repository workflow/testing guidance and adds testing conventions.