Add configurable Grafast cache limits

[Zetazzz]

Summary

Implements planning item F06 on top of the reusable performance harness in #1716.

• adds explicit per-schema limits for Grafast query, operation, and operation-plan caches
• accepts limits from pgpm.json/runtime options or three environment variables
• validates every merged configuration source as a safe integer of at least 2
• installs one schema plugin only when at least one limit is configured
• preserves Grafast upstream defaults and current behavior when omitted
• keeps this PR independent of F03 preset-composition work and all scoped-introspection/retirement changes

Configuration

{
  "graphile": {
    "grafastCache": {
      "queryCacheMaxLength": 512,
      "operationsCacheMaxLength": 256,
      "operationOperationPlansCacheMaxLength": 32
    }
  }
}

Equivalent environment variables:

• GRAPHILE_QUERY_CACHE_MAX_LENGTH
• GRAPHILE_OPERATIONS_CACHE_MAX_LENGTH
• GRAPHILE_OPERATION_PLANS_CACHE_MAX_LENGTH

Validation

Passed:

• focused cache-limit configuration tests: 19 tests
• full @constructive-io/graphql-env tests: 28 tests
• focused Grafast cache-limit plugin tests: 6 tests, including real eviction under query diversity
• full @constructive-io/graphql-server tests: 143 tests
• performance harness tests: 7 tests
• CJS and ESM builds for graphql-types, graphql-env, graphile-settings, graphql-server, and perf-harness
• pnpm install --frozen-lockfile
• ESLint on all changed TypeScript files (one pre-existing unused catch-variable warning remains in graphql-server)
• git diff --check

The full graphile-settings run passed 7 of 8 suites (67 tests). Its preset-integration suite has 29 PostgreSQL failures because the local test role lacks permission for schema integration_test. The exact same 29 failures were reproduced on the unchanged base commit 6500d408e9f0e2240f7272869f0f15bf6d12e1fa, so this is a base/environment issue rather than an F06 regression.

Refs constructive-io/constructive-planning#1693.