feat: add simulate_buy and simulate_sell view functions (#836)

[sojetunde8]

Summary

Adds simulate_buy and simulate_sell read-only view functions to the CreatorKeysContract that compute bonding curve pricing for any quantity without mutating state. This powers client-side price previews and batch buy total cost estimates.

Closes #836

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Motivation

Clients need to show price previews for various quantities without triggering a transaction. These simulation functions allow frontends to:

• Display real-time buy/sell quotes for any key quantity
• Estimate total cost before initiating a transaction
• Support batch buying workflows with accurate cost breakdowns
• Show fee breakdowns (creator fee + protocol fee) transparently

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Changes

creator-keys/src/lib.rs

New struct: SimulateResponse

#[derive(Clone, Debug, PartialEq)]
#[contracttype]
pub struct SimulateResponse {
    pub total_cost: i128,       // Total cost (buy) or net proceeds (sell)
    pub per_unit_price: i128,   // Average price per key
    pub creator_fee: i128,      // Total creator fee portion
    pub protocol_fee: i128,     // Total protocol fee portion
}

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[Chucks1093]

❌ CI Failed — verify (Contracts CI)

The verify check is failing on this PR.

Likely causes:

• Compile error from a mismatched type or unresolved import
• cargo fmt not run — CI checks formatting
• Unused variable or import triggering deny(warnings)

Steps to fix:

1. Run cargo build locally and fix all compiler errors
2. Run cargo fmt --all and commit the diff
3. Push