Solv Protocol - BTC Redemption

The `withdrawFeeRate` is an admin-controlled parameter that can be updated at any time and is applied immediately when users call the `withdrawBTCPlus()` function. Since users typically estimate their expected net `solvBTC` output off-chain before submitting a transaction, a fee update occurring shortly before execution may result in users receiving less value than anticipated. This creates a front-running-style risk where a legitimate admin fee update, applied between a user’s transaction submission and execution, may lead to reduced `solvBTC` output. Although the admin is assumed to operate in good faith, users who are unaware of recent parameter changes or rely on stale off-chain data have no on-chain protection against this behavior due to the absence of a minimum output check.

This contract acts as a rate limited redeem mechanism, imposing both total limits per time period and limits for single withdrawal actions. However, a single user could submit multiple calls to `withdrawBTCPlus()` within a single transaction to exhaust the entire total limit, which can be retrieved from `remainingWithdrawAmount()`.

The `withdrawBTCPlus()` function relies on `getValueByShares()`, which depends on the external NAV of `BTC+`. Since the NAV can legitimately increase or decrease over time, a deviation between transaction submission and execution may result in users receiving less solvBTC than expected, even without any malicious behavior.