test(rust): add deterministic test support

[blakinio]

Purpose

Implement the single authorized W3-TEST package: deterministic Rust test support consuming merged foundation and diagnostics contracts.

Delivered contract

• exactly one oteryn-test-support library crate, category tool;
• TestTimeline directly owns/clones ManualClock and provides explicit current/advance/try-set/context helpers;
• DiagnosticEventFixture accepts reviewed static message/keys and already-classified diagnostic values;
• TestSupportError wraps only closed static-text and bounded-event errors;
• compile-fail barriers reject runtime-owned message/key strings;
• deterministic tests cover time progression, clone/thread observation, backwards/overflow non-mutation, exact context, field order/bounds/duplicates and redaction.

Scope and boundaries

Only workspace-local foundation and diagnostics dependencies. No second clock, wall-clock, sleep, polling, timer wheel, async runtime, executor, scheduler, global registry, environment mutation, logger/sink, product service, protocol/auth data, assets or external-repository changes.

The architecture checker/fixtures, Rust toolchain/CI and deny policy remain unchanged.

Task

OTC-20260729-deterministic-test-support

Changed paths

Exactly ten owned/leased paths: one crate, Cargo workspace/lockfile, five owning documents and the active task record.

Validation

Exact final head: 88c98a216230d15bd9cf5d02645f618dff705f59.

Reviewed implementation head 53b4c6ac6af74ff0409c12e6daeafed86c547fae passed:

• Rust Client run 30435982581: locked metadata, fmt, Clippy, unit/doctests, architecture and Supply Chain;
• repository CI run 30435982834: all required jobs and CI / Required;
• complete ten-file/full-diff review.

The final task-record head must pass the same exact-head required graph before readiness/merge.

Compatibility claim

None. This is test-only infrastructure and proves no client runtime, server, GPU, protocol or non-Windows compatibility.