TS: static is() type guard on profile classes

[ryukzak]

Closes #146.

Summary

• Generate a static is(resource: unknown): resource is BaseType on profile classes for ergonomic collection filtering without hand-rolling resourceType predicates or relying on from() throwing.
• Emitted only for profiles that can be meaningfully discriminated:
  • resource profiles (with meta) — check resourceType + meta.profile.includes(canonicalUrl)
  • extension profiles — check url === canonicalUrl
• Skipped otherwise, since a check of only resourceType (or always-true) would be a misleading guard.

Usage

The motivating example from the issue collapses to:

const bps = (bundle.entry ?? [])
  .map(e => e.resource)
  .filter(USCoreBloodPressureProfile.is) // narrows to Observation matching this profile
  .map(o => USCoreBloodPressureProfile.apply(o));

Generated output (resource profile)

static is (resource: unknown) : resource is Observation {
    if (typeof resource !== "object" || resource === null) return false;
    const r = resource as { resourceType?: string; meta?: { profile?: string[] } };
    if (r.resourceType !== "Observation") return false;
    return (r.meta?.profile ?? []).includes(observation_bpProfile.canonicalUrl);
}

Generated output (extension profile)

static is (resource: unknown) : resource is Extension {
    if (typeof resource !== "object" || resource === null) return false;
    return (resource as { url?: string }).url === birthPlaceProfile.canonicalUrl;
}