Feat(v2): add online core models & v2 framelib generation

[KafCoppelia]

Summary

• add online v2 core/neuron enums, models, and public exports
• add float codec helpers for BF16/FP32 payload packing
• implement online v2 frame generation, payload normalization, and online weight packing
• expand model and framelib regression coverage, including pack/unpack round-trip checks
• document v2.5 online core and online neuron terminology
• bump package version from 2.0.0b1 to 2.0.0b2

[codecov]

Codecov Report

❌ Patch coverage is 96.95864% with 25 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
paicorelib/framelib/frame_gen_v2.py	91.05%	8 Missing and 9 partials ⚠️
tests/framelib/test_frame_gen_v2.py	97.77%	3 Missing and 4 partials ⚠️
tests/utils.py	94.11%	0 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
paicorelib/__init__.py	91.30% <ø> (ø)
paicorelib/core_defs_v2.py	100.00% <100.00%> (ø)
paicorelib/core_model_v2.py	100.00% <100.00%> (ø)
paicorelib/float_codec.py	100.00% <100.00%> (ø)
paicorelib/framelib/__init__.py	100.00% <100.00%> (ø)
paicorelib/framelib/frame_defs.py	100.00% <100.00%> (ø)
paicorelib/framelib/utils.py	60.31% <ø> (ø)
paicorelib/neuron_defs_v2.py	100.00% <100.00%> (ø)
paicorelib/neuron_model_v2.py	100.00% <100.00%> (ø)
tests/test_core_model_v2.py	100.00% <100.00%> (ø)
... and 5 more