Cannot import GeoJSON with NaN measurements

[petebankhead]

Bug report

Describe the bug
QuPath can (attempt to) export GeoJSON containing NaNs, but can't then read the GeoJSON it has written itself.

See https://forum.image.sc/t/qupath-object-import-via-geojson-file-error/85384 for the initial bug report.

To Reproduce
Run the following script:

def json = """
{
  "type": "Feature",
  "id": "d0852662-6941-4506-bc90-cbda1c2fa7b0",
  "geometry": {
    "type": "Polygon",
    "coordinates": [
      [
        [44196, 21480],
        [44420, 21480],
        [44420, 21687],
        [44196, 21687],
        [44196, 21480]
      ]
    ]
  },
  "properties": {
    "objectType": "annotation",
    "measurements": {
      "Anything": NaN,
      "Anything else": 2.0
    }
  }
}
"""

def po = GsonTools.getInstance().fromJson(json, PathObject)

The result is an exception

class java.lang.String cannot be cast to class java.lang.Number (java.lang.String and java.lang.Number are in module java.base of loader 'bootstrap') in QuPathScript at line number 27

ERROR: qupath.lib.measurements.MeasurementList.putAll(MeasurementList.java:234)
    qupath.lib.io.QuPathTypeAdapters$MeasurementListTypeAdapter.read(QuPathTypeAdapters.java:679)
    qupath.lib.io.QuPathTypeAdapters$MeasurementListTypeAdapter.read(QuPathTypeAdapters.java:634)
    com.google.gson.TypeAdapter.fromJsonTree(TypeAdapter.java:296)
    qupath.lib.io.QuPathTypeAdapters$PathObjectTypeAdapter.parseObject(QuPathTypeAdapters.java:535)
    qupath.lib.io.QuPathTypeAdapters$PathObjectTypeAdapter.read(QuPathTypeAdapters.java:464)
    qupath.lib.io.QuPathTypeAdapters$PathObjectTypeAdapter.read(QuPathTypeAdapters.java:280)
    com.google.gson.Gson.fromJson(Gson.java:1214)

Expected behavior
NaNs import properly... and export is also handled properly (whatever way that is).

Desktop (please complete the following information):

• OS: All
• QuPath Version: 0.4.3 (but likely before)