9.3.0

Added

• Export-PhaseTimingTreeIfRequested - the self-guarding opt-in wrapper over
  Export-PhaseTimingTree. Reads the output-path environment variable (default
  TIMING_TREE_OUTPUT_PATH, overridable via -EnvVariableName) and delegates
  to Export-PhaseTimingTree only when it is set; unset/empty, or a
  never-initialised default context, is a no-op. Centralises the env-var guard
  every child emitter (provision.ps1, create-users.ps1, remove-users.ps1,
  register-runners.ps1) previously hand-wrote at each export site, so the
  opt-in contract name lives in exactly one place - a typo can no longer
  silently disable a single consumer's export - and each call site collapses to
  one intention-revealing call. The core Export-TimingSpanTree and its shim
  Export-PhaseTimingTree stay mandatory on their path argument; the env-var
  read lives only in this opt-in-aware layer.