Add Double bridge

[roxblnfk]

Add Double integration as an alternative to Mockery.

• Wait a stable release

[roxblnfk]

Implemented on branch feature/bridge-double (monorepo, bridge/double/).

Design — mirrors the Mockery bridge: a DoublePlugin registers a DoubleInterceptor (innermost, ORDER_CLOSE_TO_TEST) that arms Double::armAutoVerify() before each test and runs Double::verifyAll() in a finally afterwards. It replaces Double's own VerifiesDoubles PHPUnit trait (which Testo can't use). Verified expectations are reported to the Assert plugin so a mock-only test isn't flagged as making no assertions.

Fibers / context switching — Double keeps its auto-verify state ($pending, $pendingReceived, $autoVerifyArmed) in process-global statics, so interleaving tests on Testo's fiber scheduler would sweep each other's doubles into the wrong teardown. The interceptor wraps the test in a trampoline fiber and snapshots/restores that global state around every suspension — the same technique the Mockery bridge uses for the Mockery container. The $states WeakMap is object-keyed and left untouched. Covered by Self (Revolt await + solo fiber) and Feature (RoundRobin interleave + Expect::exception) suites; 21 tests green on PHP 8.4.

Two open points for the Double maintainer:

1. PHP requirement. jasonmccreary/double requires php: ^8.3, but Testo's CI matrix still includes 8.2. Pulling the bridge into the monorepo therefore breaks composer install on the 8.2 leg. Options: Double lowers to ^8.2, or Testo drops 8.2 for this bridge / a dedicated 8.3+ job. Needs coordination.
2. No public seam for the pending state. The fiber isolation currently reads/writes the three private statics on Double via reflection, pinning the bridge to Double's internals (^0.6.1). A small public snapshot/reset API (or a way to run auto-verification against an externally-held collector) would remove the reflection coupling.

Pinned to jasonmccreary/double: ^0.6.1 for now (no stable 1.0 yet, per this issue).

[roxblnfk]

Progress on the two open items from above:

• Double supports PHP 8.2 — the ^8.3 constraint breaks composer install on Testo's 8.2 CI leg. Fix proposed upstream: Support PHP 8.2 jasonmccreary/double#9 (lowers to ^8.2, adds an 8.2 / PHPUnit 11 CI row).
• Public seam for Double's pending state — the bridge currently reaches into Double's private statics by reflection (Internal\GlobalState) for fiber isolation; a public snapshot/reset API would drop that coupling.

[roxblnfk]

Deferring this indefinitely and labeling it blocked.

The bridge itself is implemented and green (#298). The only blocker is the runtime requirement: jasonmccreary/double requires PHP ^8.3, while Testo's CI matrix still includes 8.2, so pulling it into the release infra breaks composer install on the 8.2 leg. The upstream fix to lower that to ^8.2 (jasonmccreary/double#9) was declined.

So there is no path to releasing testo/bridge-double without either Double relaxing its PHP requirement or Testo dropping 8.2 — neither of which is planned right now. #298 stays open with the bridge ready; this will be revisited if that changes.