Add SONATA point-process cell support

[ilkilic]

This PR adds support for SONATA point-process cells.

Point-process cells are instantiated from SONATA model_type = "point_process" and model_template, mapping directly to NEURON point mechanisms defined in HOC/MOD files.

What is included

• New HocPointProcessCell for SONATA point-process populations
• Mechanism instantiation driven by model_template (e.g. nrn:IntFire1, hoc:)
• Integration with CircuitSimulation (instantiate_gids, callbacks, deletion)
• Spike detection and recording compatible with existing simulation flow
• Support for SONATA inputs and SynapseReplay via _add_stimuli
• Compatibility with SONATA edge loading through existing SonataCircuitAccess

[codecov]

Codecov Report

❌ Patch coverage is 29.85075% with 141 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
bluecellulab/cell/point_process.py	31.34%	92 Missing ⚠️
bluecellulab/point/point_connection.py	0.00%	36 Missing ⚠️
bluecellulab/point/connection_params.py	0.00%	7 Missing ⚠️
bluecellulab/circuit_simulation.py	75.00%	6 Missing ⚠️

Files with missing lines	Coverage Δ
bluecellulab/circuit_simulation.py	85.22% <75.00%> (-1.37%)	⬇️
bluecellulab/point/connection_params.py	0.00% <0.00%> (ø)
bluecellulab/point/point_connection.py	0.00% <0.00%> (ø)
bluecellulab/cell/point_process.py	31.34% <31.34%> (ø)

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