NotEquals (`!$eq`) operator does not work

[superpowered]

The Not Equals operator either does not function as intended, or is documented incorrectly.
https://github.com/yext/search-core/blob/master/docs/search-core.matcher.md

Using the !$eq operator in any filter results in the following error:

"code": 9413,
"type": "FATAL ERROR", 
"message": "Invalid parameter: The following operator in the filters parameter is invalid: key !$eq, value: \"test\""`,
"name": ANSWERS_PARAMETER_INVALID

The Matcher enum has a remark that this value should be compatible with all field types.

/**
* A not equals comparison
* 
* @remarks
* Compatible with all field types.
*/
NotEquals = "!$eq",

Some example queries that do not work (throw the above error):

filters: {
  "c_something": {"!$eq": "test"}
}

filters: {
  "c_something": {"!$eq": 1}
}

filters: {
  "c_something": {"!$eq": true}
}

Some example queries that do work (do not throw the above error):

filters: {
  "c_something": {"$eq": "test"}
}

filters: {
  "c_something": {"$eq": 1}
}

filters: {
  "c_something": {"$eq": true}
}

an example using 'seach-headless-react':
Fails:

const test = {
  selected: true,
  filter: {
    kind: "fieldValue",
    fieldId: 'c_something',
    value: 'test',
    matcher: Matcher.NotEquals,
  }
}
searchActions.setStaticFilters([test]);

Works:

const test = {
  selected: true,
  filter: {
    kind: "fieldValue",
    fieldId: 'c_something',
    value: 'test',
    matcher: Matcher.Equals,
  }
}
searchActions.setStaticFilters([test]);

I also attempted a few other matchers to see if maybe it was incorrect in the TS api, but they also do not seem to work: $neq, $!eq