### Summary
Several endpoints related to VAAs and observations returned `null` when no results were found.
This commit changes the behavior to return `[]` instead, which is more ergonomic for users.
Endpoints affected:
- `GET /api/v1/observations/:chain`
- `GET /api/v1/observations/:chain/:emitter`
- `GET /api/v1/observations/:chain/:emitter/:sequence`
- `GET /api/v1/observations/:chain/:emitter/:sequence/:signer/:hash`
- `GET /api/v1/vaas/{chain_id}`
- `GET /api/v1/vaas/{chain_id}/{emitter}`
- `GET /api/v1/vaas/{chain_id}/{emitter}/{seq}`
### Summary
Context: https://github.com/wormhole-foundation/wormhole-explorer/issues/154
This PR modifies all endpoints that receive an emitter/guardian address to accept a wider range of formats.
After this pull request, all of these are equivalent:
* `0x000000000000000000000000f890982f9310df57d00f659cf4fd87e65aded8d7`
* `000000000000000000000000f890982f9310df57d00f659cf4fd87e65aded8d7`
* `0xf890982f9310df57d00f659cf4fd87e65aded8d7`
* `f890982f9310df57d00f659cf4fd87e65aded8d7`
### Testing plan
* Added unit tests for the parsing code.
* Tested manually a few of the affected endpoints.
### Summary
Split `/v1` and `/api/v1` controllers into different packages (respectively `api/routes/guardian` and `api/routes/wormscan`).
Still need to move services/repositories/models according to the new package layout.
agodnic
walker-16