Indexer: funding fee accrual mapping

[0xMegie]

Area: apps/s03-indexer/src/mappings/**

Goal: Cover funding accrual events that affect position accounting.

Tasks:

• Add fixtures for funding accrual/settlement events.
• Assert cumulative funding fields update deterministically.
• Assert idempotent reprocessing of the same event.

Acceptance:

• Protocol-scale values preserved as strings/BigInt.
• bun run --cwd apps/s03-indexer test passes.

[pablowizzy24]

Funding fee accrual mapping tracks and records funding fees over time, making them easy to query and analyze.

[pablowizzy24]

Funding fee accrual mapping tracks and records funding fees over time, making them easy to query and analyze.