507 add gripper to reachyjoints version2

[glannuzel]

Grippers are now listed in reachy.joints

Creation of a parallel_gripper element, Hand is now abstract and the type of hand must be specified

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
4202	2964	71%	0%	🟢

New Files

File	Coverage	Status
src/reachy2_sdk/grippers/init.py	100%	🟢
src/reachy2_sdk/grippers/gripper_joint.py	94%	🟢
src/reachy2_sdk/grippers/parallel_gripper.py	57%	🟢
tests/units/offline/test_gripper_joint.py	100%	🟢
TOTAL	88%	🟢

Modified Files

File	Coverage	Status
src/reachy2_sdk/components/antenna.py	66%	🟢
src/reachy2_sdk/orbita/orbita.py	80%	🟢
src/reachy2_sdk/orbita/orbita2d.py	74%	🟢
src/reachy2_sdk/orbita/orbita3d.py	78%	🟢
src/reachy2_sdk/parts/arm.py	39%	🟢
src/reachy2_sdk/parts/hand.py	71%	🟢
src/reachy2_sdk/parts/head.py	55%	🟢
src/reachy2_sdk/parts/part.py	84%	🟢
tests/units/offline/test_arm.py	100%	🟢
tests/units/offline/test_head.py	100%	🟢
tests/units/offline/test_orbita2d.py	100%	🟢
tests/units/offline/test_orbita3d.py	100%	🟢
tests/units/online/test_audit.py	100%	🟢
tests/units/online/test_hand.py	100%	🟢
TOTAL	82%	🟢

updated for commit: 1571ed6 by action🐍

[RemiFabre]

LGTM
Did a superficial read of the diffs, everything seems sane.
Ran jupyer notebooks 2 and 3, everything worked.