Add additional `obelisk_py` generic classes

[alberthli]

Continues the work of #20.

Additional changes besides main tasks:

• new obelisk_typing.py file created to store all relevant types for type checking and dynamic typing use-cases like in ObeliskNode. for consistency, all types are now specified as TypeVars to prevent ambiguity about what fields the types may have.
• major upgrades to ObeliskNode. Now, the core idea for configuring these nodes is that callback groups, timers, publishers, and subscribers can be configured by what is called a configuration string. This is a stringified version of the information contained in some configuration yaml file that the user supplies to launch files to bring up Obelisk nodes. This massively simplifies the creation of expected publisher/subscriber combinations in each type of node, like controllers, estimators, etc.
• allow user to manually allow non-Obelisk publishers/subscribers if they really want to for maximum flexibility
• removed workaround script in pixi.toml for downgrading pytest. Easier to just specify the pytest version as a non-pypi dependency.

Obelisk Modules

• [x] ObeliskController
• [x] ObeliskEstimator
• [x] ObeliskSensor
• [x] ObeliskRobot
• [x] ObeliskSim(ObeliskRobot)

Maintenance/Code

• [x] Separate tests into semantically different test functions cleanly - currently pretty messy
• [x] Bulk up test cases with language model suggestions
• [x] Remove JointEncoder in favor of just JointEncoders
• [x] Consider making it the standard to initialize the value of stateful quantities in on_configure instead of __init__
• [x] Remove x_hat from the attributes of the ObeliskController. Let the user manage the internals themselves.
• [x] Change default ROS config string param names to be have suffix settings instead of config_str.
• [x] Comment out auto sensor list publisher/subscriber creation in ObeliskRobot and ObeliskSensor

Future

• [ ] Add a required_fields argument to all component creation functions to enforce conditionally required fields. This is useful for, e.g., when we want to help the user make a bunch of publishers from a list of config strings.
• [ ] Potential TODO: Add checks that restrict the message types of publishers/subscribers depending on the ObeliskNode type (for instance, in the ObeliskController, we should restrict that the publisher can only publisher ObeliskControlMsg types)

[Zolkin1]

Is there a reason your ObeliskRobot doesn't implement an on_shutdown?