Replay shrunk failures via PropTestConfig.shrinkPaths + Eval index (#3076) - #6098

Part 2 of #3076, builds on top of #6097 (path recording). This PR adds the consumer side: a
PropTestConfig.shrinkPaths field that, paired with seed and skipTo, replays a previously
discovered failure directly to its shrunk value without re-running the search.

Until #6097 merges, the diff here shows both PRs' changes. After #6097 lands the diff will
narrow to just the replay infrastructure. Reviewing #6097 first is easiest.

What it does

After a failure, the message now looks like:

Property failed after 47 attempts

	Arg 0: -1 (shrunk from -32891)

Repeat this test by using seed 1234567890
Eval index: 47
Shrink paths: [[0, 2, 1]]

Caused by AssertionError: ...

To replay that exact case without re-shrinking:

forAll(PropTestConfig(
   seed = 1234567890L,
   skipTo = 47,
   shrinkPaths = listOf(listOf(0, 2, 1)),
), Arb.int()) { n -> n >= 0 }

The shrink phase skips its search and walks children[0] -> children[2] -> children[1] directly.

Pieces

• PropTestConfig.shrinkPaths: List<List<Int>>? — one path per arg. Like skipTo (added in
  Add skipTo for skipping N test cases (#4280) #4307) this lives on PropTestConfig only; the higher-level PropTest DSL does not expose it.
• doReplay walks the recorded path and runs the test once on the final node. Strict — if a
  path index is out of bounds (Shrinker changed), the final value passes (property changed), or
  it's rejected by assume(), it throws an internal ReplayShrinkPathException. Silent fallback
  would label a non-failing value as the "shrunk" case, which defeats the feature.
• handleException catches that exception and prints a Note: shrink replay was skipped — ...
  line to stdout, then continues through the normal property-failure path. Users see a regular
  property failure (seed, eval index, cause), never a leaked internal exception. The same path
  handles requireShrinkPathsArity when the supplied shrinkPaths size doesn't match the
  property's arity.
• Eval index: N is PropertyContext.evals() at failure time — the value skipTo consumes.
  The existing Property failed after N attempts line uses successes + failures which drifts
  away from evals when there are assume() skips or earlier skipTo'd iterations, so it
  can't drop into skipTo cleanly. The two values coexist now.
• shrinkfn (22 overloads) and the matching proptest call sites thread shrinkPaths through.

maxFailure > 0 lazy shrink

While integrating the catch I noticed I'd moved shrinkfn() outside the throw branches in
handleException and fixed it before pushing. The shrink/replay now runs only when the test
is actually about to fail terminally, matching pre-#3076 behavior. There's a regression test
for it ("with maxFailure > 0, the shrinker is not invoked for allowed failures...").

API / binary compatibility

• PropTestConfig gains the new field. Its JVM all-args constructor signature changes — this
  matches how skipTo was added in Add skipTo for skipping N test cases (#4280) #4307. @JvmOverloads would balloon the generated overload
  set on a data class with this many defaulted params, so I didn't add it.
• doShrinking, the public throwPropertyTestAssertionError, and all 22 shrinkfn overloads
  get @JvmOverloads so their old JVM signatures stay alongside the new ones. The api dump
  shows both.
• ReplayShrinkPathException and requireShrinkPathsArity are internal — they don't enter
  the public ABI.

Tests

• doReplay strict failure modes: out-of-bounds, negative index, final-value-passes, assume-skip
• end-to-end: extract Eval index + Shrink paths from a real failure message, feed them back
  via PropTestConfig with ShrinkingMode.Off, verify the same shrunk Arg 0 is reached. (Mode
  Off proves replay is following the path rather than searching — without the path the run would
  report the un-shrunk initial value.)
• arity mismatch + stale path both produce regular property failures, not raw exceptions
• maxFailure > 0 lazy-shrink regression
• regression updates to ForAll2Test / ForNoneTest expected messages for the new lines

Open question

The Shrink paths: [[2, 0, 1]] format was chosen so it copy/pastes cleanly into a
PropTestConfig(shrinkPaths = ...) literal. Happy to switch to per-arg lines or a different
label if you'd rather — easier to settle now than later.