chore: V8 process isolation

[NathanFlurry]

Summary

• V8 process isolation runtime with shared process model
• Docker build for linux-x64 binary
• Release script: platform package support, optionalDeps sync, --no-git-checks
• pkg-pr-new workflow updated with v8 package + Docker build

Test plan

• pkg-pr-new publishes all packages including @secure-exec/v8
• Install from pkg-pr-new URL and verify exec() works with process globals

[pkg-pr-new]

Open in StackBlitz

secure-exec

pnpm add https://pkg.pr.new/rivet-dev/secure-exec@20

@secure-exec/browser

pnpm add https://pkg.pr.new/rivet-dev/secure-exec/@secure-exec/browser@20

@secure-exec/core

pnpm add https://pkg.pr.new/rivet-dev/secure-exec/@secure-exec/core@20

@secure-exec/node

pnpm add https://pkg.pr.new/rivet-dev/secure-exec/@secure-exec/node@20

@secure-exec/python

pnpm add https://pkg.pr.new/rivet-dev/secure-exec/@secure-exec/python@20

@secure-exec/typescript

pnpm add https://pkg.pr.new/rivet-dev/secure-exec/@secure-exec/typescript@20

@secure-exec/v8

pnpm add https://pkg.pr.new/rivet-dev/secure-exec/@secure-exec/v8@20

commit: 32e80b0