Strip dev-only platform binaries from published package, remove postinstall

[gh0stonio]

Note: See #518 for a cleaner approach that replaces all platform-specific entries with a single bun devDependency and removes setup-bun.mjs entirely. This PR is kept as a lower-impact alternative.

Summary

Fixes #222

Prevents @oven/bun-* and @rollup/rollup-* platform binaries (~400MB) from being installed by SDK consumers, while keeping them available for contributors.

Builds on the investigation from #451, thanks @ochafik!

Context

At Datadog we're building on MCP Apps and this optionalDependencies bloat is blocking our CI pipelines, which motivated picking this up.

Why moving to devDependencies doesn't work

#451 moved the binaries from optionalDependencies to devDependencies. The problem is these packages declare os/cpu constraints in their own package.json. In optionalDependencies, npm silently skips platform mismatches. In devDependencies, npm ci fails hard (e.g. macOS ARM errors on @oven/bun-linux-x64).

Removing them entirely doesn't work either: contributors need the @oven/bun-* packages installed before prepare runs so that setup-bun.mjs can find and link the bun binary for the build step.

Approach

The binaries must stay in optionalDependencies for contributor installs to work, but they must not appear in the published package.json. The solution uses npm lifecycle hooks to strip them at publish time:

• prepack (runs before npm pack / npm publish): backs up package.json, then removes only @oven/bun-* and @rollup/rollup-* entries from optionalDependencies (other optional deps are preserved)
• postpack (runs after): restores the original package.json from backup

Also removes the postinstall script, which is redundant with prepare (line 64) that already runs setup-bun.mjs. The script isn't even shipped in the published package ("files": ["dist"]), so as noted in the #451 review, no INIT_CWD detection is needed.

This is a bit hacky but has the lowest impact on the contributor workflow. No build scripts or setup logic are changed.

Test plan

Verified from a clean state (rm -rf node_modules && npm ci):

• npm ci succeeds
• npm run build / npm run build:all succeed
• npm test passes (85/85)
• npm run test:e2e passes
• npm run prettier passes
• typedoc passes
• npm pack produces a tarball with no optionalDependencies in its package.json
• Local package.json is correctly restored after pack (17 optionalDependencies entries)
• Consumer install from tarball: 92 packages / 26MB, zero @oven/bun-* or @rollup/rollup-*