Make Form Fields Visible/Printable by Default (#28)

* # Make Form Fields Visible by Default

Explicitly set `/F` flag to 4 (Visible on Screen and Visible when Printed) for Textbox and Checkbox form fields.
Otherwise the content of these form fields become invisible when the document is printed.

* add venv to gitignore

---------

Co-authored-by: Alphan Aksoyoglu <alphan.aksoyoglu@deliveryhero.com>
Co-authored-by: Alphan Aksoyoglu <alphanbe@gmail.com>

Author: AlphanAksoyoglu

.gitignore

@@ -7,3 +7,4 @@ uv.lock
 *.pdf
 dist
 models/
+.venv

commonforms/form_creator.py

@@ -63,6 +63,7 @@ def __init__(
                 NameObject("/V"): TextStringObject(value or ""),
                 NameObject("/DV"): TextStringObject(default_value or ""),
                 NameObject("/Ff"): NumberObject(0 if not multiline else (1 << 12)),
+                NameObject("/F"): NumberObject(4),
                 NameObject("/Rect"): rect,
                 NameObject("/DA"): TextStringObject("/Helv 0 Tf 0 0 0 rg"),
             }
@@ -88,6 +89,7 @@ def __init__(
                 NameObject("/Subtype"): NameObject("/Widget"),
                 NameObject("/FT"): NameObject("/Btn"),
                 NameObject("/Ff"): NumberObject(0),
+                NameObject("/F"): NumberObject(4),
                 NameObject("/Rect"): rect,
                 NameObject("/V"): pdf_value,
                 NameObject("/AS"): pdf_value,