NextDouble(min, max) can return maxExclusive, and returns Infinity for wide finite bounds (Uniform distribution too) #61

What's wrong

IRandomProvider.NextDouble(minInclusive, maxExclusive) promises a value in [min, max). It is defined in Essentials/IRandomProvider.cs, around line 188:

return minInclusive + (NextDouble() * (maxExclusive - minInclusive));

This has two separate problems.

1. It can return the excluded upper bound

When the unit draw is close to 1, rounding the final addition can land exactly on maxExclusive.

• NextDouble(1.0, Math.BitIncrement(1.0)) returned maxExclusive in 495 of 1000 draws.
• The top unit draw also returns max for (1, 2), (0.3, 0.7), (5, 5.5) and (0.9, 1.0).

Callers that rely on the exclusive bound can index out of range or double-count a boundary bucket. Examples are binning, array[(int)NextDouble(0, n)]-style code, and half-open interval partitioning.

2. It overflows for finite bounds that pass validation

maxExclusive - minInclusive overflows to +Infinity when the bounds are far apart:

• NextDouble(double.MinValue, double.MaxValue) returns Infinity on every call.
• It returns NaN when the unit draw is 0, because 0 * Inf is NaN.

UniformDistributionProvider has the same flaw (Essentials.DistributionProviders.Uniform/UniformDistributionProvider.cs, around line 43, width = maximum - minimum). With new UniformDistributionProvider(-1e308, 1e308):

All of the above was reproduced with a console app against the net10.0 builds.

Suggested fix / acceptance criteria

• Clamp the result: if it is >= maxExclusive (and max > min), return Math.BitDecrement(maxExclusive).
• When the width is not finite, interpolate without computing the width, for example min * (1 - u) + max * u or 2 * (min/2 + u * (max/2 - min/2)).
• In UniformDistributionProvider:
  • compute Mean and Median as Minimum/2 + Maximum/2;
  • handle an infinite width in Cdf and Quantile the same way.
• Add tests:
  • NextDouble(1.0, Math.BitIncrement(1.0)) never returns max (a stub provider returning ulong.MaxValue makes this deterministic);
  • NextDouble(double.MinValue, double.MaxValue) is finite;
  • Uniform(-1e308, 1e308) has Mean == 0 and Cdf(0) == 0.5.