Add metric for when the file on disk is not the file being evaluated

[mlw]

Adds a new metric that tracks cases where the file reported in EXEC events is not the same file currently on disk.

Test setup: Create some binary named t. In one terminal, run the following to rapidly change t devno/inode pair:

cp t t1
cp t t2
while [[ true ]]; do rm ./t; cp ./t1 ./t; sleep 0; rm ./t; cp ./t2 ./t; sleep 0; done

In a second terminal, continuously execute the binary:

while [[ true ]]; do ./t > /dev/null; done

Sample santactl metrics output:

  Metric Name               | /santa/event_stat_change_count
  Description               | Count of times a stat info changed for a binary being evalauted
  Type                      | SNTMetricTypeCounter
  Field                     | step=MessageCreate,error=0
  Created                   | 2024-05-15T00:47:07.050Z
  Last Updated              | 2024-05-15T00:47:07.050Z
  Data                      | 70
  Field                     | step=MessageCreate,error=2
  Created                   | 2024-05-15T00:47:07.050Z
  Last Updated              | 2024-05-15T00:47:07.050Z
  Data                      | 62
  Field                     | step=NoChange,error=0
  Created                   | 2024-05-14T23:47:10.405Z
  Last Updated              | 2024-05-15T00:47:07.050Z
  Data                      | 1252973