Add read-only price query helper and unit tests for protocol fee calculation at boundary supply values

[Chucks1093]

Summary

Off-chain tools and tests both need to predict prices and fees without triggering state-mutating transactions. A read-only price query function and thorough fee unit tests at boundary supply values address both needs and together verify the bonding curve formula end to end.

Scope

• Add query_price(supply: u64) -> i128 read-only contract function — returns the same value the buy path computes for that supply step, requires no auth, performs no storage writes
• Add unit tests for query_price at supply 0, 1, and a mid-range value confirming output matches the inline formula
• Add protocol fee unit tests at supply 0, 1, and 1000 asserting the computed fee matches expected bps-based value; assert fee floors (rounds down) on non-whole stroop results

Acceptance Criteria

• query_price is read-only, requires no auth, performs no writes
• query_price output matches buy-path formula at supply 0, 1, and mid-range
• Protocol fee correct at supply 0, 1, and 1000
• Fee rounds down on non-whole stroop results
• Fee tests use configured bps, not a hardcoded percentage

ETA: 12 hours

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Coordinate on Telegram

[DingiDinigi]

I'm an experienced Rust/Web3 developer with Soroban smart-contract experience, including bonding curve mechanics and read-only query design. I've reviewed the bonding curve/buy-path implementation — adding a stateless query_price alongside boundary-value fee tests closes a real gap for off-chain tools that currently can't predict pricing without simulating a mutating call.
I'll implement query_price(supply: u64) -> i128 mirroring the buy path's exact formula with no auth and no storage writes, and test it at supply 0, 1, and a mid-range value against the inline formula. For protocol fees, I'll test supply 0, 1, and 1000 against the configured bps (not a hardcoded percentage), and specifically assert the floor/round-down behavior on non-whole stroop results, since that's the kind of edge case that silently breaks accounting if missed.

I can deliver within the 12-hour window, with full test output included in the PR description. kindly assign to me.

[dev-king-001]

Good day maintainer, can you assign me this.

[edehvictor]

Hi maintainers!
I’d love to help out with this issue. I’ve checked the current codebase/documentation and know exactly what needs to be updated to make this clearer. I will ensure everything aligns perfectly with your existing contribution guidelines.

[grantfox-oss]

🦊 GrantFox — @edehvictor has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #572)
2. Your PR will be reviewed by the accesslayerorg maintainers

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