add Bun.YAML.parse to types

[dylan-conway]

What does this PR do?

How did you verify your code works?

[robobun]

^{Updated 4:59 PM PT - Aug 25th, 2025}

❌ @dylan-conway, your commit 3212926 has 6 failures in Build #23889:

• test/integration/mysql2/mysql2.test.ts - timeout on 🍎 13 aarch64
• test/js/third_party/body-parser/express-memory-leak.test.ts - timeout on 🐧 12 x64-asan
• test/js/web/request/request-clone-leak.test.ts - timeout on 🐧 12 x64-asan
• test/js/node/test/parallel/test-gc-http-client-connaborted.js - timeout on 🐧 3.21 x64-baseline
• test/js/bun/shell/shell-load.test.ts - 1 failing on 🐧 12 x64-asan
• test/js/bun/shell/shell-load.test.ts - 1 failing on 🍎 14 x64
• test/js/bun/shell/shell-load.test.ts - 1 failing on 🍎 13 x64
• test/js/bun/shell/shell-load.test.ts - 1 failing on 🐧 24.04 x64-baseline
• test/bundler/compile-windows-metadata.test.ts - 1 failing on 🪟 2019 x64-baseline
• test/bundler/compile-windows-metadata.test.ts - 1 failing on 🪟 2019 x64

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🧪   To try this PR locally:

bunx bun-pr 22129

That installs a local version of the PR into your bun-22129 executable, so you can run:

bun-22129 --bun

[kravetsone]

What about generic

[alii]

@kravetsone We're going with unknown for now, for two reasons:

• Familiarity with JSON.parse (not exactly, but developers often do JSON.parse(val) as MyType, which would be the same here.
• Gives us the option to change it in the future with minimal breakages to existing consumers

We considered the generic approach of parse<T = unknown>(value: string): T but it's basically the same as casting but a less familiar API, while being equally-unsafe.

[kravetsone]

@kravetsone We're going with unknown for now, for two reasons:

• Familiarity with JSON.parse (not exactly, but developers often do JSON.parse(val) as MyType, which would be the same here.
• Gives us the option to change it in the future with minimal breakages to existing consumers

We considered the generic approach of parse<T = unknown>(value: string): T but it's basically the same as casting but a less familiar API, while being equally-unsafe.

Thanks! Yea I guess as approach is good enough for this