Support integer-typed numerical attributes and heuristic measurements

[copybara-service]

Support integer-typed numerical attributes and heuristic measurements

NumericalInitializer changes:

• For integer-typed attributes, snap quantile edges to the integer
  lattice via floor().
• Set upper=max_value+1 so edges can reach max_value after floor,
  allowing the last bin to capture concentrated mass there. Edges at
  max_value are removed from bin_edges and their count absorbed into
  the last bin's weight.
• Use positive jitter U(0, 0.5) for integer data so that integer
  points are never pushed across a boundary before floor.
• Add _zcdp_rho property derived from the composed dp_event.
• Accept an optional estimated_total in call(). When provided,
  construct a heuristic LinearMeasurement assuming uniform counts
  across original bins with stddev = 1/sqrt(rho).

vectorized_transformations changes:

• Format integer bin intervals as [low, high] (closed-closed) instead
  of (low-1, high] (open-closed) for readability.