feat: add rlimits (resource limits) support for sandboxes

[zmarty]

• Add rlimits field to sandbox configuration and CLI arguments
• Support resource limits in format RLIMIT_NAME=soft:hard (e.g., RLIMIT_NOFILE=16384:65536)
• Update API documentation with rlimits examples
• Add rlimits support to MCP server
• Extend server handler to process rlimits configuration
• Update all relevant CLI binaries and configuration builders

WARNING: I am not a Rust developer and this is vibe coded. It works, but it needs review and it needs to be closed out by someone more familiar with the codebase.

Fixes #284

[appcypher]

Hey @zmarty, thanks for the contribution.
I'm going to review it and give you feedback, it might just take a couple days to get to it.

[appcypher]

I have reviewed this PR btw. I’m holding off on merging for now because there are other features and fixes I’ll be batching together, and some of the changes are related to this one.

[chemeris]

Hi, @appcypher, any chance this could be merged?
I'm also facing heavy "too many open files" issues. Basically, I can't run anything because I'm getting "too many open files" as soon as I try.

[appcypher]

@chemeris I'm making ground up changes to microsandbox but I haven't gotten to it yet.
This pr handles some part of it but it is not complete. Until then, I can't merge this pr.
Also can't make a commitment because I just don't know when I will have time to fix these issues.