Add compute budget estimation utility for all contract functions

[Kingsman-99]

Overview

Callers have no way to estimate the instruction count or memory usage of contract calls before submitting them. Add a simulation-based estimation utility and document budget limits for all public functions.

Acceptance Criteria

• estimate_compute(function_name, args) off-chain utility function using soroban_simulation
• Returns { instructions: u64, mem_bytes: u64, read_entries: u32, write_entries: u32 }
• Estimation covers all public contract functions: create_invoice, pay_invoice, release_funds, get_invoice, get_leaderboard, get_stats
• COMPUTE_BUDGETS.md documents measured instruction counts for typical inputs (1 recipient, 5 recipients, 20 recipients)
• Warning emitted in tests if any function exceeds 80% of the Soroban instruction limit
• CI benchmark job runs estimation on each PR and posts a budget table as a PR comment
• Any function exceeding the instruction limit fails CI

[sheyman546]

@sheyman546 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

please i will love work on this issue

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[emteebug12-jpg]

@emteebug12-jpg has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

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.

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[brite-side0]

@brite-side0 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

hello dear maintainer i would love to work along side you on this task sir.

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Congratulations, @brite-side0! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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This issue has been completed by @brite-side0 as part of the Stellar Wave Program's 6th Wave 🥳

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