dmap, deterministic map iterator order for DST

I needed deterministic map iteration order

for my deterministic simulation testing (using the

new testing/synctest package -- experimental in go1.24, but 

proposal approved to move forward, yay!) so I wrote a "dmap" which 

provides repeatably ordered full range scan for keys

that can be turned into strings.

The cost is about 3x the memory.  However since dmap is an order 

of magnitude faster than the built in Go map for repeated full-

range scans, dmap still may be of general interest:

You would need to extract these two files from the larger project (a few seconds work).

Enjoy.

                                                                                                                            
go test -v -bench=BenchmarkDmapVsBuiltin -run=blah
faketime = false
goos: darwin
goarch: amd64
pkg: github.com/glycerine/rpc25519
cpu: Intel(R) Core(TM) i7-1068NG7 CPU @ 2.30GHz
BenchmarkDmapVsBuiltin
BenchmarkDmapVsBuiltin/Set
BenchmarkDmapVsBuiltin/Set/Dmap
BenchmarkDmapVsBuiltin/Set/Dmap-8 48343575         22.36 ns/op
BenchmarkDmapVsBuiltin/Set/Builtin
BenchmarkDmapVsBuiltin/Set/Builtin-8 75154516       15.51 ns/op
BenchmarkDmapVsBuiltin/Get
BenchmarkDmapVsBuiltin/Get/Dmap
BenchmarkDmapVsBuiltin/Get/Dmap-8 62711772        18.13 ns/op
BenchmarkDmapVsBuiltin/Get/Builtin
BenchmarkDmapVsBuiltin/Get/Builtin-8 100000000       10.89 ns/op
BenchmarkDmapVsBuiltin/Delete
BenchmarkDmapVsBuiltin/Delete/Dmap
BenchmarkDmapVsBuiltin/Delete/Dmap-8 3335937        359.3 ns/op
BenchmarkDmapVsBuiltin/Delete/Builtin
BenchmarkDmapVsBuiltin/Delete/Builtin-8 27277524       39.09 ns/op
BenchmarkDmapVsBuiltin/Range
BenchmarkDmapVsBuiltin/Range/Dmap
BenchmarkDmapVsBuiltin/Range/Dmap-8 316316             3477 ns/op << nice
BenchmarkDmapVsBuiltin/Range/Dmap_ordercache
BenchmarkDmapVsBuiltin/Range/Dmap_ordercache-8 2099700      560.4 ns/op << very nice
BenchmarkDmapVsBuiltin/Range/Builtin
BenchmarkDmapVsBuiltin/Range/Builtin-8 144405               7922 ns/op
PASS
ok github.com/glycerine/rpc25519 11.701s