feat: integrate price fetching functionality with new PriceFetcher mo…

[Oluwasuyi-Timilehin]

#closes #736

Description

This PR implements an off-chain price fetcher in the data-processing module to support the Soroban pricing adapter contract on testnet. The new implementation fetches USD prices for XLM and USDC, scales them to the pricing adapter contract's base decimals (10^7), and includes fallback and stale-cache handling for failed source calls.

Changes Made

1. New Price Fetcher Module

• Added apps/data-processing/src/ingestion/price_fetcher.py
• Supports primary CoinGecko price fetch and fallback CoinCap fetch
• Handles request failures by returning stale cached payloads when available
• Produces adapter-ready payloads with:
  • asset_code
  • asset_issuer
  • price_usd
  • price (scaled to 10^7)
  • asset_decimals
  • base_decimals
  • source
  • timestamp
  • is_stale
  • success

2. Pipeline Integration

• Integrated PriceFetcher into apps/data-processing/src/main.py
• Fetches price data in parallel with news, on-chain volume, and network stats
• Prints price feed status during pipeline runs
• Includes price_feed in the pipeline result output

3. Tests

• Added apps/data-processing/tests/test_price_fetcher.py
• Covers:
  • successful price fetch and scaling
  • stale cache fallback when sources fail
  • error payload when no source and no cache are available

4. Dependency and tooling

• Installed runtime dependency support for requests and stellar-sdk in the project test environment
• Verified module imports and test execution in the data-processing package

Acceptance Criteria Met

✅ Supports XLM and USDC asset pricing

✅ Produces scaled prices aligned with adapter decimals (10^7)

✅ Handles stale/failed source fallback with cached values

Validation

• python -m pytest -q tests/test_price_fetcher.py

Files Changed

• apps/data-processing/src/ingestion/price_fetcher.py
• apps/data-processing/src/ingestion/__init__.py
• apps/data-processing/src/main.py
• apps/data-processing/tests/test_price_fetcher.py

Notes

• The new price fetcher is currently limited to the supported asset list in SUPPORTED_ASSETS.
• Future enhancements may include additional supported issued assets and storing price feed results in a persistent cache or ledger.

#closes

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