feat: add xidl to ECOSYSTEM.md

[cathaysia]

Motivation

Unify the Axum error model, handle Axum boilerplate code, and generate OpenAPI.

Solution

1. install xidlc:

cargo binstall xidlc

2. write a idl:

interface SmartCityHttpApi {
    @get(path = "/v1/stops/{stop_id}{?line,lang}")
    string get_stop_eta(
        string stop_id,
        string line,
        string locale,
        out uint32 eta_seconds,
        out string destination
    );

    @get(path = "/v1/stops/{stop_id}/nearby")
    sequence<string> list_nearby_stops(
        @path("stop_id") string stop_id
    );
}

3. generate code

xidlc -l axum api.idl --server --client
xidlc -l openapi api.idl

Thanks!

[davidpdrsn]

As of #3737 we've decided to remove ECOSYSTEM.md. See that PR for more details.