[Gui] fix some CI warnings

- narrowing conversion from 'unsigned long' to signed type 'int' is implementation-defined
- floating point literal has suffix 'f', which is not uppercase
- narrowing conversion from 'double' to 'float'
- Slots named on_foo_bar are error prone
- also tome Clang style fixes

(see here for the reports: https://github.com/FreeCAD/FreeCAD/pull/7522/commits/d9c2efcc)

src/Gui/DlgRunExternal.cpp

@@ -116,7 +116,7 @@ void DlgRunExternal::finished (int exitCode, QProcess::ExitStatus exitStatus)
     ui->buttonAbort->setEnabled(false);
 }
 
-void DlgRunExternal::on_chooseProgram_clicked()
+void DlgRunExternal::onChooseProgramClicked()
 {
     QString fn;
     fn = QFileDialog::getOpenFileName(this, tr("Select a file"), ui->programPath->text());