add optional, nullable, nullish, default and coerce to schemas

[pxseu]

Adds schema modifiers that were missing (IMO) from k:

• .optional() — accepts undefined, dropped from the OpenAPI required list
• .nullable() / .nullish() — accept null / null | undefined
• .default(value) — falls back to value when undefined, surfaced as default in OpenAPI
• k.coerce.number() — parses numeric strings before the usual number checks (query params, form data)

object, ref and objectFromURLSearchParams honour optional & default fields when parsing/serializing. A genuinely-missing required property still errors with Missing required property as before. Tests added for each.

const user = k.object({
  id: k.coerce.number(),        // "1" -> 1
  name: k.string(),
  bio: k.string().optional(),
  role: k.string().default('user'),
});

I used them successfully before in https://github.com/pxseu/pxseu.com (as a patch), and they came in clutch honestly.…les, make getContext and onError optional, move server options into the router to require less boilerplate, add openapi example

[vercel]

@pxseu is attempting to deploy a commit to the otters Team on Vercel.

A member of the Team first needs to authorize it.

[alii]

Sorry we cannot support undefined as a value in kschema. The semantics for optional are going to be difficult. I have some changes somewhere that implement my desired behaviour. I'll follow up once I have time to work on that