Add CurrentTickAccount — an oracle-owned PDA (one per price source) that holds
the latest raw tick written by the price source and a timestamp. The price source
calls UpdateCurrentTick after each price-changing operation; anyone can then call
RecordTick (upcoming) to advance the PriceObservations accumulator without
requiring the price source to be present. PDA is derived from price_source_id
only (no window) since a single current tick serves all time windows.
Add price_to_tick(price: u128) -> i32 to twap_oracle_core: isqrt(price << 128)
-> sqrtPriceX96 -> get_tick_at_sqrt_ratio. The sqrtPriceX96 is clamped to
>= MIN_SQRT_RATIO so a zero/dust price maps to MIN_TICK rather than erroring.
Add a pure-integer integer_sqrt(U256) (bit-by-bit, no floating point): ruint's
root is gated behind its std feature and seeds with f64, neither available in
the guest. Uses wrapping_shr for the digit loop (checked_shr rejects the
intended lossy shifts).
Pull in uniswap_v3_math (for get_tick_at_sqrt_ratio) and alloy-primitives
(U256), with ruint pinned to =1.17.0 — 1.18 raised its MSRV to rustc 1.90,
above the risc0 guest toolchain's 1.88.
