fix: lxml 4.x.x issue on python 3.14

[Alchez]

I get the following error when trying to install a Frappe app that uses this SDK:

Using Python 3.14.4 environment at: env
Resolved 9 packages in 527ms
      Built electronic-payments @ file:///erpn/apps/electronic_payments
  × Failed to build `lxml==4.9.4`
  ├─▶ The build backend returned an error
  ╰─▶ Call to `setuptools.build_meta:__legacy__.build_wheel` failed (exit status: 1)

      In file included from /tmp/xmlXPathInitqigypd7l.c:1:
      /usr/include/libxml2/libxml/xpath.h:561:21: note: declared here
        561 |                     xmlXPathInit                (void);
            |                     ^~~~~~~~~~~~
      error: command '/usr/bin/x86_64-linux-gnu-gcc' failed with exit code 1

      hint: This usually indicates a problem with the package or the build environment.
  help: `lxml` (v4.9.4) was included because `electronic-payments` (v15.8.3) depends on `authorizenet` (v2.0.0) which depends on `lxml`