feat: Add comprehensive tests and snapshots for key quote functionali…

[testersweb0-bug]

Summary

This PR introduces standardized quote formatting and read-only quote views for the creator-keys contract. It ensures consistency between buy and sell quote responses while enabling callers to retrieve accurate pricing and fee breakdowns without mutating contract state.

Closes #55
Closes #56
Closes #57

Key Changes

1. Standardized Quote Formatting

• Added QuoteResponse struct (Clone, Debug, PartialEq, contracttype)
• Implemented shared format_quote_response helper to unify buy/sell quote structure
• Standardized calculation logic:
  • Buy → total = price + fees
  • Sell → total = price - fees

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2. Read-Only Quote Methods

• Added get_buy_quote

  • Returns total payment required for next key purchase
  • Includes full fee breakdown
  • Does not mutate contract state

• Added get_sell_quote

  • Returns sell value and fee breakdown
  • Rejects with InsufficientBalance if holder has zero keys

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3. Test Coverage

• Added comprehensive tests for:
  • get_buy_quote
  • get_sell_quote
• Covered edge cases:
  • Zero holder balance
  • Missing config
  • Invalid creator state

Testing

• cargo fmt --all -- --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo test --workspace

Checklist

• Linked issue or backlog item
• Contract behavior and invariants are described clearly
• Docs updated if contract interfaces or workflows changed
• Scope stays limited to one contract concern

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