fix(Request) isolate body usage

[cirospaciari]

What does this PR do?

Just a refactoring isolating the usage of Request body this is the first step necessary for #23327 please review #23319 first

How did you verify your code works?

CI

[robobun]

^{Updated 2:10 AM PT - Oct 7th, 2025}

❌ @cirospaciari, your commit 754c316 has 1 failures in Build #28332 (All Failures):

• test/integration/bun-types/bun-types.test.ts - 6 failing on 🪟 2019 x64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🪟 2019 x64-baseline
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 3.21 aarch64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 12 aarch64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 24.04 aarch64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 25.04 aarch64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 12 x64-asan
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 3.21 x64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 24.04 x64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 25.04 x64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 25.04 x64-baseline
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 12 x64-baseline
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 24.04 x64-baseline
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 12 x64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🐧 3.21 x64-baseline
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🍎 14 x64
• test/integration/bun-types/bun-types.test.ts - 6 failing on 🍎 13 x64

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🧪   To try this PR locally:

bunx bun-pr 23326

That installs a local version of the PR into your bun-23326 executable, so you can run:

bun-23326 --bun