Fix default size settings in `plot.Layout`

[ArtemkaKun]

Describe the bug

Currently default values for plot.Layout are

pub struct Layout {
pub mut:
	title       string
	title_x     f64  = 0.5
	autosize    bool = true
	width       int  = 550
	height      int  = 550
	xaxis       Axis
	yaxis       Axis
	annotations []Annotation
}

both autosize and width/height are defined, and autosize is set to true which makes no sense since it wouldn't be taken into account because of width/height are not 0.

Expected Behavior

autosize is set to false by default

Current Behavior

autosize is set to true while width/height are not 0 by default

Reproduction Steps

Not related

Possible Solution

No response

Additional Information/Context

No response

V version

V 0.4.2 f54f156.20a1af3

Version used

6904d72

Environment details (OS name and version, etc.)

Not related