TS: accept all FHIR literal reference forms in Reference<T>

[ryukzak]

Closes #141.

Changes

• Widen the generated Reference<T>.reference field from `${T}/${string}` to a union that covers every form allowed by FHIR references: relative, absolute http/https, urn:uuid, urn:oid, and #fragment.
• Add a demo in examples/typescript-r4/resource.test.ts that assigns each literal form to a typed Reference field, so the widened union is exercised by tsc.
• Regenerate src/fhir-types and the typescript-r4 / typescript-us-core example fhir-types.

Before / after

Motivation: Reference<"Patient"> was rejecting urn:uuid placeholders used in transaction Bundles, forcing an inline cast that lies about the string's shape.

Before:

export interface Reference<T extends string = string> extends Element {
    reference?: `${T}/${string}`;
}

const patientUrn = `urn:uuid:${randomUUID()}`;
const bp = USCoreBloodPressureProfile.create({
    status: "final",
    // ❌ TS2322: Type 'string' is not assignable to type `Patient/${string}`
    subject: { reference: patientUrn },
});

After:

export interface Reference<T extends string = string> extends Element {
    reference?:
        | `${T}/${string}`
        | `http://${string}`
        | `https://${string}`
        | `urn:uuid:${string}`
        | `urn:oid:${string}`
        | `#${string}`;
}

// compiles — no cast required
const bp = USCoreBloodPressureProfile.create({
    status: "final",
    subject: { reference: patientUrn },
});