Implement `Experiment` and API

[szabo137]

Description:

Introduce an Experiment type to represent collider and multi-beam experiments within the LaserExperiments.jl package.
An experiment combines one or more beams (e.g. an AbstractLaserBeam and/or an ElectronBeam) and may exist as either a generic or a deployed instance.

Requirements:

• Each experiment must have:

  • a name (unique identifier)
  • a list of participating beams (Vector{AbstractBeam}; could include lasers or electrons)
  • a type or flag indicating whether it is generic or deployed

• For deployed experiments:

  • a facility field to indicate where the experiment is located
  • an optional status field (e.g. "commissioned", "running", "finished")

Proposed API:

# Generic experiment definition
exp = Experiment(
    name = "GammaRaySource",
    beams = [laserbeam(...), electronbeam(...)],
    kind = :generic
)

# Deployed experiment linked to a facility
exp_deployed = Experiment(
    name = "GammaRaySource_HiBEF",
    beams = [laserbeam(...), electronbeam(...)],
    kind = :deployed,
    facility = "HiBEF",
    status = :running
)

Tasks:

• Define Experiment struct and related constructors
• Integrate experiment storage into the registry system
• Add comprehensive unit tests and example entries

Notes:
This structure should generalize to any number of participating beams, allowing the same API to describe both collider and multi-laser setups.