feat: add 'poolKey' to create worker

[kallebysantos]

Towards FUNC-905

What kind of change does this PR introduce?

Feature

What is the current behavior?

Today, the runtime reuses a cached worker based on the servicePath. Two functions in the same folder could wrongly get served by each other's cached worker, and it doesn't allow purging the current code.

What is the new behavior?

Introduces the poolKey, a new optional field you can pass to control that caching yourself, instead of relying on the folder path. Leave it out and nothing changes.

Example

// Bump poolKey on each deploy to force a fresh worker:
await EdgeRuntime.userWorkers.create({
  servicePath: "./functions/my-func",
  poolKey: `my-func:${deploymentVersion}`,
});

// Or give two functions the same poolKey to intentionally share one worker:
await EdgeRuntime.userWorkers.create({ servicePath: "./functions/a", poolKey: "shared-key" });
await EdgeRuntime.userWorkers.create({ servicePath: "./functions/b", poolKey: "shared-key" }); // reuses a's worker

[satyarohith]

LGTM 👍

[aantti]

Cc @luizfelmach