perf(apigateway): read the account singleton once per provider

[jasonrowsell]

Stacked on #6911 — the first two commits are that PR; review just the last one.

Every ApiGatewayV1/ApiGatewayWebSocket registers its own Read of the API Gateway account, and Pulumi re-reads each from AWS on every up, diff, and refresh. The account is a per-provider singleton, so on an app with 35 gateways that's 40 identical AWS calls per deploy. Deduplicating them cut a no-change pulumi up from 35s to 22s on our largest app.

This memoizes the read per provider (lazy + Map, same pattern as useProvider):

• Same provider → one shared read; dependsOn ordering for stages/log groups unchanged.
• Multiple providers → one read each, with suffixed logical names so URNs stay unique.
• Provider via providers (plural) or inheritance → unchanged: the read stays on the default provider, as today.
• Existing stacks → the surplus reads are external Read resources, so they drop out of state on the next deploy with no AWS calls.
• Fresh-account bootstrap from fix(apigateway): duplicate CloudWatch role URN on fresh accounts #6911 untouched — APIGatewayAccountSetup keeps its name, role singleton unchanged.

Added platform/test/components/apigateway-account.test.ts covering read identity per provider and URN uniqueness across providers. It deliberately skips the import "../../src/global.d.ts" line — that file runtime-imports @types/node, which breaks vitest collection in the suites that include it.