Migrate all 32-byte hash fields from TEXT (64-char hex) to BLOB
(32 bytes) for ~50% storage savings on hash columns.
Changes:
- Add src/db/blob.rs with ToBlob/FromBlob traits for hash types
- Update all table schemas to use BLOB for hash columns
- Replace .to_hex() with .to_blob() for DB inserts
- Replace ::from_hex() with ::from_blob() for DB reads
- Use SQL hex() function where API responses need hex strings
- Bump DB_VERSION from 4 to 5
Affected tables: tx, pool, pool_history_entry, utxo_spending,
utxo_funding, user_action, auth_chain_entry, bcmr_data,
bcmr_failure, bcmr_well_known, crc20, crc20_candidates,
delphi_entry, cached_token_metrics
Fixes#1
Introduce CachedJson response wrapper with cache duration based on data mutability:
- CACHE_IMMUTABLE (1 day): historical data with explicit timestamps
- CACHE_BCMR (5 min): token metadata
- CACHE_AGGREGATE (60s): aggregate data that changes with blocks
- CACHE_NONE: real-time data (current price, active pools, latest txs)
Endpoints dynamically select cache duration based on whether time parameters
are explicitly provided (historical/immutable) or defaulted to now (live).
Return proper 4XX status codes for client errors to prevent load balancers
from misinterpreting input validation failures as server errors. Add
centralized ApiResult type and ApiErrorCode enum for consistent handling.
