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dart - Unwanted space appearing between RaisedButton widgets in a column

tl;dr Why is space appearing between my two buttons when I have not explicitly set any?

I am trying to make a layout like the one below:

Image depicting a basic mobile login page consisting of a centered column containing a logo and two vertically-stacked buttons underneath for login and registration. There is some space between the logo and the buttons but no space between the buttons

However, what appears to be about 16px of space appears between the two buttons and I cannot figure out where it is coming from.

I at first thought maybe the Column was adding space but I am using MainAxisAlignment.center which shouldn't add any. I now think that there is perhaps some Material theming going on that automatically applies padding to the RaisedButton, however I have looked through both button_theme.dart and raised_button.dart and it seemed like only the inner padding (between text and button edges) was being set. I'm sure I overlooked something and would appreciate any help in finding out why this space exists.

auth.dart (screen shown in the image)

...
Widget build(BuildContext context) {
return Scaffold(
    backgroundColor: Colors.white,
    body: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          Expanded(flex: 2, child: Container()),
          Expanded(
              flex: 8,
              child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  crossAxisAlignment: CrossAxisAlignment.center,
                  children: [
                    Padding(
                        padding: EdgeInsets.fromLTRB(0, 0, 0, 32),
                        child: Image(
                            fit: BoxFit.contain,
                            image: AssetImage('lib/res/drawable/logo.webp'))),
                    PrimaryButton(
                        onPressed: //...,
                        child: Text('Log In')),
                    PrimaryButton(
                        onPressed: //...,
                        child: Text('Sign Up')),
                  ])),
          Expanded(flex: 2, child: Container()),
        ]));
}

primary_button.dart (custom rounded button widget that extends RaisedButton):

...
Widget build(BuildContext context) {
return Theme(
    data: Theme.of(context).copyWith(
      textTheme: Theme.of(context).textTheme,
      buttonTheme: Theme.of(context).buttonTheme.copyWith(
          padding: EdgeInsets.all(0),
          minWidth: double.infinity,
          buttonColor: Theme.of(context).accentColor,
          shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(24))),
    ),
    child: Builder(builder: super.build));
}
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add the property materialTapTargetSize and set it to MaterialTapTargetSize.shrinkWrap.

materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,

if you check the source code of RawMaterialButton it adds a padding based on that value:

    Size minSize;
        switch (widget.materialTapTargetSize) {
          case MaterialTapTargetSize.padded:
            minSize = const Size(48.0, 48.0);
            break;
          case MaterialTapTargetSize.shrinkWrap:
            minSize = Size.zero;
            break;
        }

        return Semantics(
          container: true,
          button: true,
          enabled: widget.enabled,
          child: _InputPadding(
            minSize: minSize,
            child: result,
          ),
        );

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