[nexus] Accept DiskSource::{Image, Snapshot}s without read_only

[hawkw]

@ahl rightly points out that the common case for the disk_create APIs is to create read-write disks, and it seems like kind of a drag to require all calls to create a read-write disk from an image or snapshot to include a "read_only": false field in the JSON body. Thus, this commit adds #[serde(default)] so that disk source params without a "read_only" are the same as "read_only": false.

Unfortunately, we didn't catch this until after #9731 merged, so fixing it the proper way requires a whole new API version. Since the conversion between the Rust params types in nexus-types is trivial, it might have been possible to bend the rules a bit here and just tweak the previously-generated API version to make the field nullable --- clients operating with the slightly-older version of that version would still always be accepted since they would always send the field. But, bending the rules makes me scared I'm gonna get in trouble, so I did it the proper way, at the expense of a whole lot of code that does basically nothing.

[david-crespo]

Looks fine to me. Can’t believe the conversions. In theory it could be fine to just overwrite the old version since nobody is running the previous version. It does feel completely ridiculous to have to do this.

[david-crespo]

Confirmed it has the desired effect on the TS client:

--- a/2026013001.0.0-1c5abd/Api.ts
+++ b/2026013100.0.0-c09e48/Api.ts
@@ -1920,7 +1920,7 @@
   /** Create a disk from a disk snapshot */
   | {
       /** If `true`, the disk created from this snapshot will be read-only. */
-      readOnly: boolean;
+      readOnly?: boolean;
       snapshotId: string;
       type: "snapshot";
     }
@@ -1928,7 +1928,7 @@
   | {
       imageId: string;
       /** If `true`, the disk created from this image will be read-only. */
-      readOnly: boolean;
+      readOnly?: boolean;
       type: "image";
     }
   /** Create a blank disk that will accept bulk writes or pull blocks from an external source. */
@@ -7484,7 +7484,7 @@
    * Pulled from info.version in the OpenAPI schema. Sent in the
    * `api-version` header on all requests.
    */
-  apiVersion = "2026013001.0.0";
+  apiVersion = "2026013100.0.0";
 
   constructor({ host = "", baseParams = {}, token }: ApiConfig = {}) {
     this.host = host;