[PeerX Backlog # 8] Add a `tracing`-based test-logging harness in CI

[ameeribro4-sudo]

Problem Statement
The contract supports soroban_sdk::events as the only observability
surface. Tests collapse all events into a single stream and a failing
assertion cannot easily be tied to a specific event sequence.

Why it matters
For property-based invariant testing and fuzzing, deterministic replay
of failed sequences is essential.

Expected Outcome
Tests can be replayed with --nocapture --test-threads=1 against a
deterministic ledger so any invariant failure reproduces bit-for-bit.

Acceptance Criteria

• Jest-style test artifacts (CARGO_TARGET_TMPDIR/timing) are published.
• An example test (swap_invariant) demonstrates the harness.

Implementation Notes
Use env.ledger().with_mut(|l| { l.timestamp = … }) — already exercised
in rate_limit.rs:sensitive_tests.

Files Affected

• peerx-contracts/counter/Cargo.toml ([features] test-determinism).
• Several *_tests.rs modules.

Dependencies Issue #1.
Difficulty / Effort 🥈 / S
Labels ci, testing, dx

[OTimileyin]

Failing assertions in the current test suite can't be tied to a specific event sequence, making invariant failures hard to reproduce deterministically.

Plan: add a test-determinism feature gate in counter/Cargo.toml, wire deterministic ledger timestamps via env.ledger().with_mut() (matching the pattern in rate_limit.rs), publish Jest-style timing artifacts to CARGO_TARGET_TMPDIR, and add a swap_invariant example test demonstrating the harness. Tests will reproduce bit-for-bit under --nocapture --test-threads=1. PR up within a couple of days.

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #8)
2. Your PR will be reviewed by the OpenPeerX maintainers

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[grantfox-oss]

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@OTimileyin's PR #112 was approved and merged by @ameeribro4-sudo.

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👏 Great work, @OTimileyin! Keep contributing to OpenPeerX.