feat: acp client provider

[michaelneale]

this is a first pass of what an acp client as provider would look like, this lets you do things like:

GOOSE_PROVIDER=acp GOOSE_MODEL=claude ./target/release/goose run -t 'list files'
GOOSE_PROVIDER=acp GOOSE_MODEL=codex ./target/release/goose run -t 'list files'
GOOSE_PROVIDER=acp GOOSE_MODEL='npx @zed-industries/claude-code-acp' ./target/release/goose run -t 'list files'

and it uses the underlying agent to do the work, with some handling of tool responses (tools from the acp agent side, sessions etc from goose side)