Can we do EigerTriggerInfo via load/save instead?

[coretl]

It is defined here to be the standard TriggerInfo, but with energy too, so that it can be done all in one go.

ophyd-async/src/ophyd_async/epics/eiger/_eiger.py

Lines 10 to 11 in 4f4458c

	class EigerTriggerInfo(TriggerInfo):
	energy_ev: float = Field(gt=0)

We should discuss with @DominicOram and @olliesilvester if we still need that approach after #697. This will depend on what exactly is slow in the Eiger.