[Testing] Add property-based fuzz tests for MockEnvBuilder using arbitrary crate

[ekelemepraise-code]

Summary

The MockEnvBuilder accepts a wide range of inputs (sequence numbers, timestamps, balances) that could produce edge-case panics. Property-based testing with arbitrary would catch these before users encounter them.

Scope

Test the following properties:

1. Sequence/Timestamp monotonicity — at_sequence(u32::MAX) should not panic
2. Account balance overflow — very large Stroops values are handled gracefully
3. Duplicate account names — second .with_account("alice", ...) either overwrites or errors predictably
4. Empty symbol string — .with_token("", 6) fails with a clear message

Implementation

Add to contracts/crucible/src/tests.rs or a new contracts/crucible/tests/property.rs:

use arbitrary::Arbitrary;

#[derive(Arbitrary, Debug)]
struct EnvConfig {
    sequence: u32,
    timestamp: u64,
    accounts: Vec<(String, u64)>,
}

fn roundtrip(config: EnvConfig) {
    // should never panic, regardless of inputs
    let _ = MockEnv::builder()
        .at_sequence(config.sequence)
        .at_timestamp(config.timestamp)
        .build();
}

Acceptance Criteria

• arbitrary added as dev-dependency
• At least 5 property tests covering edge cases listed above
• CI runs property tests with cargo test

[onyemaechiezekiel9]

@onyemaechiezekiel9 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello, I have gone through the issue and I would love to work on this swiftly

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[To0yeni]

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[CHKM001]

@CHKM001 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

I can and will get this done within the next 3 hrs and will emrge before the wave ends
Thank you for the opportunity

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[Olamidepy]

@Olamidepy has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Kindly assign boss

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