signalEntity lower cases entity id

When I tried to signal an entity from another entity, I was able to successfully but for the wrong entityId (it looks like casing matters, and the id was becoming "mycounter", all lowercase.

In an entity:
```
const entityId = new df.EntityId("MyCounter", "scenario");
context.df.signalEntity(entityId, "add");
```

In a durable client function:
```
// This was never hit
const entityId = new df.EntityId("MyCounter", "scenario");
const { entityState } = await client.readEntityState(entityId);
```

Start by reproducing the casing example with EntityId("MyCounter", "scenario"), then trace the signalEntity and readEntityState entry points to see where the entity ID is lowercased. Done means signaling and reading both address the original case-sensitive ID, so the durable client function reaches the entity state.

Written by the indexing model from the issue text.