fix: lp api handler for stop

[snadrus]

Related Issues

Proposed Changes

implement an API handler like Worker does, but Provider-specific. Enable "stop" call for CLI to work.

Additional Info

I reused the endpoint shape that Common uses, so the client uses the Common API even though other funcs available to it will not work here.

Checklist

Before you mark the PR ready for review, please make sure that:

• Commits have a clear commit message.
• PR title is in the form of of <PR type>: <area>: <change being made>
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  • area, e.g. api, chain, state, market, mempool, multisig, networking, paych, proving, sealing, wallet, deps
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• Tests exist for new functionality or change in behavior
• CI is green

[magik6k]

yay generics exist now; We could drop the other ones now, but that's a separate PR, not now