feat(workspace): add Maritime as a sandboxed workspace backend

[mariagorskikh]

Is your feature request related to a problem?
AgentScope workspaces can run on E2B, Daytona, OpenSandbox, Docker, K8s, Apple Container and Bubblewrap. Maritime (maritime.sh) runs cloud sandboxes with the same shape as E2B's base template (Ubuntu, user user, /home/user, passwordless sudo, python3, curl), and they pause when idle and resume on the next call with disk and memory intact. There is no Maritime workspace today.

Describe the solution you'd like
A MaritimeWorkspace and MaritimeBackend under src/agentscope/workspace/_maritime/, plus MaritimeWorkspaceManager under app/workspace_manager/, following the E2B backend file for file:

• exec_shell maps to the SDK's Sandbox.run with an argv array (no shell quoting), cwd, and a timeout clamped to Maritime's 1 to 3600 seconds.
• read_file and write_file map to Sandbox.files.
• Reattachment by agentscope.workspace.id metadata through sandboxes.list(metadata=...); close() pauses, unclaimed pre-warmed sandboxes are killed, as in the E2B manager.
• The same gateway bootstrap as E2B (uv, gateway venv, agentscope --no-deps).

New dependency
An optional extra workspace-maritime = ["maritime>=0.10.0"], lazily imported. The maritime package has no third-party dependencies. It would also join the workspace extra like the others; happy to leave it out of that if you prefer.

Tests and docs
Live tests skipped unless MARITIME_API_KEY is set (mirroring the E2B ones), mocked unit tests for the SDK mapping, reattachment and the manager's pre-warm handling, and a companion "Maritime" tab in building-blocks/workspace/run-workspace.mdx in agentscope-ai/docs.

Disclosure: I'm a co-founder of Maritime. We'd maintain this backend and answer issues about it. The implementation is ready on my fork (main...mariagorskikh:agentscope:maritime-workspace). If this sounds good, I'd like to take it on once there is an issue to claim.