#2645 Codegen/Cloudflare: create-only required fields block read methods in generated Cloudflare models

Follow-up to swamp-club #2287, which fixed this for GCP in PR 341 (codegen/gcp/pipeline.ts nonCreatePathParams, and the create/update templates in codegen/gcp/extensionModelGenerator.ts).

swamp validates the whole GlobalArgsSchema whenever any global argument is set. This generator emits fields that only the create request needs as required there, so read-only methods fail unless callers pass placeholder create values.

Apply the same rule as #2287:

• Keep required only what a non-create method reads from globalArgs, plus synthetic instance names.
• Make create-only required fields optional in GlobalArgsSchema.
• Enforce them with a generated check at the start of create that throws create requires global arguments: before any API call.
• Where update fully replaces the resource (PUT), fill those fields from globalArgs, then from stored state, and throw before the API call if neither has them.
• Regenerate the provider twice (the second run must produce zero diff) and update the provider's design doc.

Required-ness is decided in buildGlobalArgsProperties in codegen/cloudflare/extensionModelGenerator.ts, from createRequired in codegen/cloudflare/pipeline.ts.

Notes:

• account_id and zone_id handling is emitted separately and must stay unchanged: required for single-scope resources, an either-or optional pair otherwise.
• The synthetic name stays required.
• The nested-object requiredSet path is unrelated.
• codegen/cloudflare/factoryAware_integration_test.ts is the natural place for an integration test.
• codegen/designs/cloudflare.md GlobalArgs notes need updating.