9.1.0

Added

• Timing-tree framework (New-TimingSpanTree, Initialize-TimingSpanTree,
  Measure-TimingSpan, Add-TimingSpanDuration) - an arbitrary-depth,
  context-owned nested span model with by-name accumulation and sticky-Failed
  status. Generalises the provisioner's 2-level phase-timing framework so
  timings can nest to any depth and, later in the feature, cross the process
  boundary.
• Export-TimingSpanTree / Import-TimingSpanTree - the cross-process
  handoff for the timing tree. Export serialises a context's whole tree to
  the versioned nested-JSON schema (e2e-timing/v1; explicit children[],
  first-class status, invariant-culture numbers); Import rebuilds it into
  an in-memory subtree, tolerating a missing or malformed file (returns
  $null with a warning, never throws) so a crashed child never fails the
  parent's own report.
• Write-TimingSpanReport - renders a timing context or a bare node subtree
  as a depth-indented, single-colour (DarkGreen) console block: per span a
  fixed-width [OK]/[FAILED]/[SKIPPED]/[RUNNING] tag, invariant-culture
  F2 seconds, and percent of its parent's effective elapsed, closed by a
  total observed line for the root. The arbitrary-depth, merge-aware
  counterpart of the provisioner's 2-level Write-PhaseTimingReport; a
  SKIPPED node shows a dash and no percent, and the total counts the root's
  effective elapsed (top-level spans, no sub-step double-count).
• 2-level phase-timing compat shims (Initialize-PhaseTimings,
  Invoke-WithPhaseTimer, Invoke-WithSubStepTimer, Add-SubStepDuration,
  Write-PhaseTimingReport) - the provisioner's pre-generalisation timing
  surface, re-expressed as thin wrappers over the timing-tree core and a
  single module-scoped default context so existing call sites keep their exact
  signatures (no -Tree argument). Behaviour-preserving: the verbs throw on
  the same undeclared-phase / not-initialised conditions and
  Write-PhaseTimingReport emits the byte-identical legacy report (fixed
  banner, no percent column, top-level-only total). Lets a consumer migrate to
  one framework without rewriting call sites.