Optimise the traversal iterators

[krcb197]

At the moment all the traversal iterators are generated explicitly, for example the following definition of a registers:

reg {
        default sw = rw;
        default hw = r;
        field { fieldwidth=8; } basicfield_h;
        field { fieldwidth=8; } basicfield_i;
        field { fieldwidth=8; } basicfield_j;
        field { fieldwidth=8; } basicfield_k;
    } basicreg_e;

results in the following code:

    @property
    def fields(self) -> Iterator[Union[FieldReadOnly, FieldWriteOnly,FieldReadWrite]]:
        """
        generator that produces has all the fields within the register
        """
        yield self.basicfield_h
        yield self.basicfield_i
        yield self.basicfield_j
        yield self.basicfield_k
        
        # Empty generator in case there are no children of this type
        if False: yield

    
    @property
    def readable_fields(self) -> Iterator[Union[FieldReadOnly, FieldReadWrite]]:
        """
        generator that produces has all the readable fields within the register
        """
        yield self.basicfield_h
        yield self.basicfield_i
        yield self.basicfield_j
        yield self.basicfield_k
        
        # Empty generator in case there are no children of this type
        if False: yield
    

    
    @property
    def writable_fields(self) -> Iterator[Union[FieldWriteOnly, FieldReadWrite]]:
        """
        generator that produces has all the writable fields within the register
        """
        yield self.basicfield_h
        yield self.basicfield_i
        yield self.basicfield_j
        yield self.basicfield_k
        
        # Empty generator in case there are no children of this type
        if False: yield

This could be improved by including code in the library to self-examine itself using vars and filter out the correct types