Add a stat DSL function

[johnkerl]

For #1559.

Example:

cat stat-test.csv

path
mlr
./mlr
Makefile
.
..
/tmp/

mlr --c2p --from stat-test.csv put '$stat = stat($path)["size"]'

path     stat
mlr      38391584
./mlr    38391584
Makefile 4110
.        1440
..       1568
/tmp/    384

$ mlr --c2j --from stat-test.csv put '$stat = stat($path)'
[
{
  "path": "mlr",
  "stat": {
    "name": "mlr",
    "size": 38391584,
    "mode": 0755,
    "modtime": 1715207874,
    "isdir": false
  }
},
{
  "path": "./mlr",
  "stat": {
    "name": "mlr",
    "size": 38391584,
    "mode": 0755,
    "modtime": 1715207874,
    "isdir": false
  }
},
{
  "path": "Makefile",
  "stat": {
    "name": "Makefile",
    "size": 4110,
    "mode": 0644,
    "modtime": 1711459625,
    "isdir": false
  }
},
{
  "path": ".",
  "stat": {
    "name": ".",
    "size": 1440,
    "mode": 020000000755,
    "modtime": 1715208111,
    "isdir": true
  }
},
{
  "path": "..",
  "stat": {
    "name": "..",
    "size": 1568,
    "mode": 020000000755,
    "modtime": 1715003072,
    "isdir": true
  }
},
{
  "path": "/tmp/",
  "stat": {
    "name": "tmp",
    "size": 384,
    "mode": 020004000777,
    "modtime": 1715191674,
    "isdir": true
  }
}
]