E2B SDK 2.56.0 requires Node.js 22 and moves to undici 8

The E2B 2.56.0 release requires Node.js 22.19.0 or newer, and the changelog says Node.js 20 is no longer supported. The package now depends only on undici 8, with undici 7 dropped.

According to the changelog, undici 8 respects the server's HTTP/2 SETTINGS_MAX_CONCURRENT_STREAMS and opens more connections when one is saturated. The SDK's own in-flight request cap is removed, along with the E2B_API_INFLIGHT_REQUESTS, E2B_ENVD_INFLIGHT_REQUESTS and E2B_ENVD_RPC_INFLIGHT_REQUESTS variables.

Concurrency is now governed by undici's connection pools, which are configured through E2B_API_CONNECTIONS and E2B_ENVD_RPC_CONNECTIONS. The release also updates @e2b/dockerfile-utils to 0.1.1.

Agents and services running on Node.js 20 or earlier will need to upgrade before they can use this version of the SDK.

Code that set the removed in-flight request variables will no longer limit requests that way, so concurrency needs to be tuned with the connection pool settings instead.