feat(network-subgraphs): Add idAsString field

[teogeb]

Added new field to Stream entity: Stream#idAsString. It has same value as in the id field. The field allows us to do substring queries for the field id (by using idAsString_contains where clause).

This feature is needed e.g. in streamr-dev/network#3132.

[Copilot]

Pull Request Overview

Add a new idAsString field to the Stream entity to support substring GraphQL queries on stream IDs.

• Set idAsString when streams are created or backfilled in both handleStreamCreation and handleStreamUpdate.
• Update the GraphQL schema to include idAsString: String! @index with a descriptive comment.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/network-subgraphs/src/streamRegistry.ts	Assign idAsString in creation and update handlers; handle backfill case.
packages/network-subgraphs/schema.graphql	Add idAsString field with index annotation and description.

Comments suppressed due to low confidence (2)

packages/network-subgraphs/src/streamRegistry.ts:50

• In the fallback branch of handleStreamUpdate, add stream.updatedAt = event.block.timestamp to ensure the new entity has both createdAt and updatedAt set consistently.

stream.createdAt = event.block.timestamp

packages/network-subgraphs/schema.graphql:39

• Consider adding integration or unit tests to verify that idAsString_contains queries return the expected subset of streams.

idAsString: String! @index