feat!: port property tests to effect/unstable/arbitrary

[BleedingDev]

Effect migration | Existing port

Why the change

Effect removed effect/testing/FastCheck, so the property-test helpers must use effect/unstable/arbitrary to work with current Effect releases.

Special things to note

• This breaks the fastCheck option in favor of arbitrary and raises the Effect peer floor to 4.0.0-rc.113.
• Exact-head CI passes typechecking, 105 runtime tests with 6 skips, ESM/declaration builds, and 36 type tests with 64 assertions on TypeScript 5.9.3 and 6.0.3.
• Release classification remains upstream's decision; the current release-please configuration proposes 1.0.0 for this breaking change.

Change outline

 property test
-  Schema.toArbitrary(input)(FC)
-  FC.tuple / FC.record / FC.assert
+  Arbitrary.schema(input)
+  Arbitrary.all / Arbitrary.checkEffect
+  formatCheckFailure for failed properties

 options
-  fastCheck: { numRuns: 5, seed: 1001 }
+  arbitrary: { runs: 5, seed: 1001 }