Add articulation and robot joint limit APIs

[yuecideng]

Description

This PR adds articulation-level joint position, velocity, and effort limit getters plus DexSim-backed setters, and exposes matching robot APIs with backward-compatible name handling and joint_ids support.

Motivation and context:

• unify joint limit API naming between Robot and Articulation
• add direct support for DexSim set_joint_limits, set_joint_velocity_limit, and set_joint_effort_limit
• keep limit caches synchronized after drive updates and cover the behavior with regression tests

Dependencies: None.

Issue reference: N/A

Verification:

• pytest tests/sim/objects/test_articulation.py tests/sim/objects/test_robot.py -q (62 passed)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Enhancement (non-breaking change which improves an existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (existing functionality will not work without user modification)
• Documentation update

Screenshots

N/A

Checklist

• I have verified the modified files are formatted with black.
• I have made corresponding changes to the documentation
• I have added tests that prove my feature works
• Dependencies have been updated, if applicable.

[Copilot]

Pull request overview

This PR extends EmbodiChain’s simulation object layer by adding articulation-level joint limit getters/setters (position/velocity/effort) with DexSim-backed writes, and exposes matching robot APIs that support both control-part (name) selection and explicit joint_ids filtering while preserving prior precedence behavior.

Changes:

• Added Articulation.get_*_limits(...) and Articulation.set_*_limits(...) APIs with env_ids/joint_ids filtering, input shape coercion, and cache updates.
• Updated Articulation.set_qpos(...) to clamp against per-environment joint position limits (instead of using a single env’s limits).
• Added Robot limit getters/setters that support joint_ids, keep backward-compatible name precedence, and are covered by new regression tests.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
tests/sim/objects/test_robot.py	Adds regression tests validating Robot limit APIs for control parts, joint_ids, and setter precedence.
tests/sim/objects/test_articulation.py	Adds comprehensive tests for limit getter/setter filtering, cache synchronization, failure behavior, and qpos clamping.
embodichain/lab/sim/objects/robot.py	Introduces a shared joint-id resolution helper and adds Robot limit getters/setters delegating to Articulation.
embodichain/lab/sim/objects/articulation.py	Implements limit caching in ArticulationData, adds limit getter/setter APIs, and updates clamping/cache sync behavior.

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