`allunique(::AbstractRange)` is fooled by very small `step`

[mcabbott]

The range defined in #58138 seems to fool unique and allunique:

julia> start = 0.7071067811865475;

julia> len = 1449;

julia> r1 = range(start, nextfloat(start), len) # works -- from 58138
0.7071067811865475:7.667286081665445e-20:0.7071067811865476

julia> unique(collect(r1))  # this is fine
2-element Vector{Float64}:
 0.7071067811865475
 0.7071067811865476

julia> allunique(r1)  # this is wrong
true

julia> collect(unique(r1))  # follows from allunique
1449-element Vector{Float64}:
 0.7071067811865475
 0.7071067811865475
 0.7071067811865475
 0.7071067811865475

[mbauman]

This is yet another case of "what does a range mean?"

#56479.