Use Bun for dependency management

[PaulRBerg]

Refs:

• Move away from PNPM v2-core#759
• build: switch to bun for dep management sablier-integration-template#3

[razgraf]

This isn't possible at the moment as the repository currently uses two package managers: Envio needs pnpm, the subgraphs are built using yarn.

I've tried updating to pnpm at some point but the subgraph projects weren't very happy about it (something to do with the extended tsconfig).

As soon as Envio starts supporting bun we can circle back to this issue. It's important we use only one package manager so we can refactor the codebase to promote re-usability between subgraphs and indexers.