feat: create a backend to parse USPTO patents into DoclingDocument (#606)

* feat: add PATENT_USPTO as input format

Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>

* feat: add USPTO backend parser

Add a backend implementation to parse patent applications and
grants from the United States Patent Office (USPTO).

Signed-off-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>

* refactor: change the name of the USPTO input format

Change the name of the patent USPTO input format to show the typical format (XML).

Signed-off-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>

* refactor: address several input formats with same mime type

Signed-off-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>

* refactor: group XML backend parsers in a subfolder

Signed-off-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>

* chore: add safe initialization of PatentUsptoDocumentBackend

Signed-off-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>

---------

Signed-off-by: Cesar Berrospi Ramis <ceb@zurich.ibm.com>
Signed-off-by: Cesar Berrospi Ramis <75900930+ceberam@users.noreply.github.com>