tests: add Soroban budget profiling to SmartAccount tests

[alberto-crossmint]

tests: add Soroban budget profiling to SmartAccount tests

Summary

Integrates budget profiling into unit tests that invoke SmartAccount contract functions to track CPU instructions and memory bytes consumed during contract execution. Adds budget snapshot utilities and instruments key contract operations across auth, plugin, policy, and signer management tests.

Changes:

• Added BudgetSnapshot struct and helper functions (budget_snapshot, print_budget_delta) in test_utils.rs
• Instrumented __check_auth calls in auth_test.rs to measure authorization overhead
• Added profiling around plugin operations (install_plugin, uninstall_plugin) in plugin_test.rs
• Instrumented signer management operations (add_signer, revoke_signer, update_signer) in signer_management_test.rs
• Added budget tracking for policy-related operations in policy_test.rs

Example budget output:

[Budget] check_auth cpu_insns=333000 mem_bytes=0
[Budget] install_plugin cpu_insns=28128 mem_bytes=5510
[Budget] uninstall_plugin cpu_insns=55619 mem_bytes=7980
[Budget] add_signer:admin3 cpu_insns=1092 mem_bytes=704

Review & Testing Checklist for Human

• Verify Soroban SDK budget API usage: Confirm env.cost_estimate().budget(), cpu_instruction_cost(), and memory_bytes_cost() are correct for soroban-sdk v22 (API was debugged during implementation but should be double-checked)
• Run tests locally: Execute cargo test -- --nocapture and verify budget output lines appear and show reasonable CPU/memory numbers
• Spot check budget measurements: Review a few "[Budget]" output lines to ensure values make sense relative to operation complexity

Notes

• Budget measurements capture deltas around contract operations but may include some test overhead alongside pure contract execution costs
• All existing tests continue to pass with identical behavior; only adds non-intrusive budget logging
• Session: https://app.devin.ai/sessions/b86f602434fb4829b881f8d0819525d1
• Requested by: Alberto García (@alberto-crossmint)

[devin-ai-integration]

Original prompt from Alberto

The task is to integrate budget profiling into unit tests that call contract functions. This will allow for granular profiling of CPU and memory consumption using the Soroban Rust SDK's budget utilities.

- For unit tests that invoke contract functions, add code to query or print the budget.
- Utilize `env.cost_estimate().budget()` or `env.budget()` (for older versions) to access the budget tracker.
- The goal is to record and display CPU instructions and bytes of memory used by contract calls.

To submit the work, ensure the changes are applied to the relevant unit test files within the stellar-smart-account repository in the smart account contract. Provide a report detailing the files modified and an example of the budget output.

You only need to look in the following repo: Crossmint/stellar-smart-account

[devin-ai-integration]

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