Prevent duplicate connections from repeated Session.open() calls

[CritasWang]

Summary

• make Connection.open() return immediately when already connected
• share an in-flight connection attempt across concurrent open() calls
• clear the in-flight state after failure so a later open() can retry
• allow CommonJS imports for generated Thrift modules and use a portable timeout type

Testing

• npm run test:unit -- --runInBand
• npm run build
• npx eslint eslint.config.mjs src/connection/Connection.ts tests/unit/Connection.test.ts (0 errors)