over 1000 packages starting with `S`

#78672 happened again. About 1 year later
We once again have over 1000 packages starting with `S` causing github not to display all folders

Options from #78672
1. Move to 2 layers of folders: `A/B/Abacus.jl`
1. Move to 2 letter prefixes: `Ab/Abacus.jl`
1. ~~Move all JLLs to own folder~~ (done)

Either of these options would shunt the problem down the road for a few more years

Here is break down of the states for counting up packages by the first two letters of their names:
(ignoring cases where there are none)

```julia
julia> using DataStructures, StatsBase

julia> packages = sort([lowercase(x["name"]) for (_,x) in TOML.parsefile("Registry.toml")["packages"] if dirname(dirname(x["path"]))!="jll"]);

julia> summarystats(collect(values(counter(x[1:2] for x in packages))))
Summary Stats:
Length: 486
Missing Count: 0
Mean: 19.197531
Std. Deviation: 35.549154
Minimum: 1.000000
1st Quartile: 2.000000
Median: 4.000000
3rd Quartile: 19.000000
Maximum: 302.000000

julia> for (x,y) in counter(x[1:2] for x in packages)
y>100 && println("$x=>$y")
end
sp=>134
bi=>116
te=>106
mo=>127
di=>173
co=>302
se=>101
qu=>122
si=>167
pr=>111
ge=>150
re=>205
in=>156
mi=>101
gr=>103
st=>224
li=>125
po=>164
ma=>162
da=>103
pa=>128
tr=>110
fi=>108
me=>110
```

Start by reading the referenced issue #78672 and the package paths in Registry.toml. Review the provided package-count analysis and compare the listed folder-layout options. Done means selecting and implementing a registry layout that avoids GitHub hiding folders once a name prefix exceeds 1,000 packages.

Written by the indexing model from the issue text.