fix(flashloan): correct Aave V3 BSC PoolDataProvider + tolerate truncated getReserveData (closes #419)

[obchain]

Summary

Two related defects on the Aave V3 BSC flash-loan path that together silenced the only flash-loan source on every fork demo and live run:

1. `config/default.toml` and `config/fork.toml` baked the PoolDataProvider as `0x41393e5e337606dc3821075Af65AeE84D7688CBD` — that address has no code on BSC mainnet (`cast code` returns `0x`). Calls returned an empty buffer, surfaced as `buffer overrun` decode errors at every quote step.
2. With the right data provider in place, `getReserveData` returns 12 fields on BSC, not the 15 our `sol!` ABI declares (newer-Aave fields `accruedToTreasury`, `unbacked`, `isolationModeTotalDebt` absent on BSC). Strict typed decoder still rejected the truncated tuple.

Fix

• Update both configs to `0xc90Df74A7c16245c5F5C5870327Ceb38Fe5d5328` (sourced via `IPoolAddressesProvider.getPoolDataProvider()` on BSC).
• Add `read_uint256_first_word` helper for `getReserveData` — we only consume the leading `configuration` word for paused/frozen bitmap, so issue the call ourselves and lift first 32 bytes. `getReserveConfigurationData` stays on typed decode (its 10-tuple matches BSC).

Test plan

• `cargo check` clean.
• Combined with fix(venus): tolerate 96-byte uint256 view returns from BSC vTokens (closes #418) #420 (Venus adapter: borrowBalanceStored decode fails with ReserveMismatch on BSC vTokens (96-byte returns) #418 venus fix), `replay --block 91323624` reports `tracked=4 returned=4 liquidatable=4 queued=4 emitted=4` (was `queued=0`).
• All four opportunities emit JSON with `simulation_result=ok` and positive `predicted_net_profit_usd_cents`.