feat: add distribution shape computation to Lockup indexer

[PaulRBerg]

Problem

The Lockup indexer lacks information about the distribution shapes of vesting streams. This forces the UI to perform these computations in the client app, meaning:

1. Computations are re-run constantly in each user's browser
2. Third-party integrations cannot access shape information
3. External developers must rewrite the algorithms to infer shapes

Solution

Compute and store distribution shapes in the indexer so the computation runs once and the data is available to everyone via the GraphQL API.

References

• Stream Shapes Documentation
• Vesting Gallery