fix(sdk): cache realtime-stream create response per (runId, key) #6224

Job	Run time
e2e / 🧪 CLI v3 tests (windows-latest - pnpm)	24s
typecheck / typecheck	16s
e2e / 🧪 CLI v3 tests (ubuntu-latest - npm)	16s
e2e / 🧪 CLI v3 tests (windows-latest - npm)	27s
sdk-compat / Bun Runtime	14s
e2e / 🧪 CLI v3 tests (ubuntu-latest - pnpm)	16s
sdk-compat / Deno Runtime	17s
sdk-compat / Cloudflare Workers	14s
sdk-compat / Node.js 22.12 (ubuntu-latest)	17s
sdk-compat / Node.js 20.20 (ubuntu-latest)	14s
units / packages / 🧪 Unit Tests: Packages (1, 1)	15s
units / internal / 🧪 Unit Tests: Internal (6, 8)	15s
units / internal / 🧪 Unit Tests: Internal (4, 8)	21s
units / internal / 🧪 Unit Tests: Internal (5, 8)	17s
units / internal / 🧪 Unit Tests: Internal (1, 8)	19s
units / internal / 🧪 Unit Tests: Internal (3, 8)	19s
units / internal / 🧪 Unit Tests: Internal (2, 8)	19s
units / internal / 🧪 Unit Tests: Internal (7, 8)	14s
units / internal / 🧪 Unit Tests: Internal (8, 8)	15s
units / webapp / 🧪 Unit Tests: Webapp (5, 8)	16s
units / webapp / 🧪 Unit Tests: Webapp (2, 8)	14s
units / webapp / 🧪 Unit Tests: Webapp (7, 8)	14s
units / webapp / 🧪 Unit Tests: Webapp (1, 8)	17s
units / webapp / 🧪 Unit Tests: Webapp (3, 8)	19s
units / webapp / 🧪 Unit Tests: Webapp (6, 8)	17s
units / webapp / 🧪 Unit Tests: Webapp (8, 8)	16s
units / webapp / 🧪 Unit Tests: Webapp (4, 8)	17s
units / packages / 📊 Merge Reports	14s
units / webapp / 📊 Merge Reports	14s
units / internal / 📊 Merge Reports	17s
	8m 24s

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