Improve Value and PathElement String()

[apelisse]

PathElements are frequently turned into strings to find out if a path has already been evaluated. Values are part of PathElements so they are also turned into strings. That's a non-negligible improvement.

benchmark                                   old ns/op     new ns/op     delta
BenchmarkOperations/Pod/Update-12           384166        329574        -14.21%
BenchmarkOperations/Node/Update-12          576277        498512        -13.49%
BenchmarkOperations/Pod/Apply-12            543377        482016        -11.29%
BenchmarkOperations/Node/Apply-12           764054        684379        -10.43%
BenchmarkOperations/Endpoints/Apply-12      2065245       1997567       -3.28%
BenchmarkOperations/Endpoints/Update-12     55470         53943         -2.75%

benchmark                                  old allocs     new allocs     delta
BenchmarkOperations/Node/Update-12         1155           967            -16.28%
BenchmarkOperations/Node/Apply-12          1876           1581           -15.72%
BenchmarkOperations/Pod/Update-12          843            727            -13.76%
BenchmarkOperations/Pod/Apply-12           1179           1024           -13.15%
BenchmarkOperations/Endpoints/Apply-12     3142           3043           -3.15%

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[lavalamp]

PathElements are frequently turned into strings to find out if a path has already been evaluated

Where? This shouldn't be done?

[lavalamp]

We should just store the path or path element and use Less (and/or use or implement Equals if not already).

[apelisse]

Will replace with something else.