[envpool] upgrade direct dependencies and remove stale mirrors

[Trinkle23897]

Summary

• Problem: EnvPool still pinned several direct Python and native dependencies to old versions, and WORKSPACE still referenced the retired https://ml.cs.tsinghua.edu.cn/~jiayi/envpool mirror.
• Scope: keep the retained first-round upgrades only: MuJoCo / dm_control versions, Python requirement floors and lockfiles, selected direct native archive versions (pybind11, glog, googletest, zlib), and matching docs / build-file updates. This PR intentionally excludes the experimental second-round Bazel / toolchain / broader C++ dependency bumps.
• Outcome: the retained direct dependency set is newer and consistent across Bazel archives, Python lockfiles, MuJoCo build outputs, and docs, and the stale mirror URLs are removed.

This narrows the dependency refresh to the direct changes that are easiest to review and keep, while dropping the more invasive toolchain work.

Technical Details

• Approach: update the direct dependency versions in workspace0.bzl and pip requirement files, regenerate the Linux lockfiles, and sync MuJoCo shared-library names plus doc references to the retained versions.
• Code pointers:
  • envpool/workspace0.bzl: removes the stale mirror URLs and bumps the retained native archive versions.
  • third_party/pip_requirements/requirements-dev.txt: updates the dev/runtime dependency inputs that feed the lockfiles.
  • envpool/mujoco/BUILD: updates the generated MuJoCo shared library output to match 3.6.0.
• Notes: I temporarily explored a second round of Bazel / toolchain / C++ dependency upgrades during debugging, but rolled those changes back before publishing this PR.

Test Plan

Automated

• brix ssh dev-0 -C -- '<targeted bazel test run on the retained first-round dependency set>': earlier targeted dev validation passed the core buffer tests plus MuJoCo / dm_control alignment tests for the retained dependency-refresh path.

Suggested Manual

• brix ssh dev-0 -C -- 'cd /root/code/envpool && bazel test //envpool/mujoco:mujoco_gym_deterministic_test //envpool/mujoco:mujoco_gym_align_test //envpool/mujoco:mujoco_dmc_suite_deterministic_test //envpool/mujoco:mujoco_dmc_suite_align_test --test_output=errors': revalidate the final PR branch on Linux.
• rg -n "ml\\.cs\\.tsinghua\\.edu\\.cn/~jiayi/envpool" envpool/workspace0.bzl: confirm the retired mirror URL is gone.

[chatgpt-codex-connector]

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