Better error forwarding in `expect_snapshot()`

[hadley]

f <- function() g()
g <- function() h()
h <- function() stop("!")

library(testthat)
test_that("", {
  local_edition(3)
  expect_snapshot(f())
})
#> ── Error:  ─────────────────────────────────────────────────────────────────────
#> Error in `h()`: !
#> Backtrace:
#>     ▆
#>  1. └─testthat::expect_snapshot(f())
#>  2.   └─testthat:::expect_snapshot_(...)
#>  3.     ├─base::withRestarts(cnd_signal(state$error), muffle_expectation = function() NULL)
#>  4.     │ └─base (local) withOneRestart(expr, restarts[[1L]])
#>  5.     │   └─base (local) doWithOneRestart(return(expr), restart)
#>  6.     └─rlang::cnd_signal(state$error)
#> Error:
#> ! Test failed with 1 failure and 0 successes.

^{Created on 2025-11-03 with reprex v2.1.1}

How can we get the original traceback here?