construct the URI path and query via typed Url

this probably either does too much or too little:
- could have fixed the double-slash thing by stripping trailing slash from the base uri or,
- if you like typed URLs, it probably makes sense to do a bigger refactor toward them.

...sidestepping adding the actual `url` dependency by using the one included with `reqwest`. maybe this is not what you want.

currently using `EncodeError::Other` instead of adding a variant to `EncodeError` itself because the parse error comes from `Url`, which we snuck in from `reqwest`, which isn't a dependency of the `-common` crate.

crates/jacquard/src/client.rs

···
 use std::future::Future;
 
 use bytes::Bytes;
-pub use error::{ClientError, Result};
+pub use error::{ClientError, Result, TransportError};
 use http::{
     HeaderName, HeaderValue, Request,
     header::{AUTHORIZATION, CONTENT_TYPE, InvalidHeaderValue},
···
     R: XrpcRequest,
     C: XrpcClient + ?Sized,
 {
-    // Build URI: base_uri + /xrpc/ + NSID
-    let mut uri = format!("{}/xrpc/{}", client.base_uri(), R::NSID);
+    // Configure the XRPC endpoint
+    let mut url: reqwest::Url = client
+        .base_uri()
+        .parse()
+        .map_err(|e| error::EncodeError::Other(format!("failed to parse base_uri: {e}").into()))?;
+    url.set_path(&format!("/xrpc/{}", R::NSID));
 
     // Add query parameters for Query methods
     if let XrpcMethod::Query = R::METHOD {
         let qs = serde_html_form::to_string(&request).map_err(error::EncodeError::from)?;
         if !qs.is_empty() {
-            uri.push('?');
-            uri.push_str(&qs);
+            url.set_query(Some(&qs))
         }
     }
 
···
         XrpcMethod::Procedure(_) => http::Method::POST,
     };
 
-    let mut builder = Request::builder().method(method).uri(&uri);
+    let mut builder = Request::builder().method(method).uri(&url.to_string());
 
     // Add Content-Type for procedures
     if let XrpcMethod::Procedure(encoding) = R::METHOD {