docs(slime): update docs for slime + sglang 0.5.13, remove useless sglang patches

[lyzustc]

This PR includes docs and installation setup update for slime commit fa3c990:

• Slime environment installation could be done by either using official docker or the provided instlaation script src/agentcore_rl_toolkit/backends/slime/scripts/install_slime.sh.
• Now we do not need to apply custom patches at all due to changes in rllm-model-gateway (feat(gateway): add use_sglang mode in model gateway that translates upstream agent's /chat/completions requests to sglang server or sgl-router endpoint's /generate requests, required for RL training with sglang (e.g. slime) rllm-org/rllm#715), delete them.
• Change the tested package version information in docs.
• Remove the LinearCrossEntropyModule parallelism error info from troubleshooting page as it is addressed in new slime.

See updated docs page at https://lyzustc.github.io/agentcore-rl-toolkit/.

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