Support Push and Pop global items in report descriptor parsing

[Nortaq-PlayNexus]

Support Push (0b1010) and Pop (0b1011) global items

Summary

The HID specification defines two global item tags that save and restore the global item state table (HID 1.11, sections 6.2.2.7 and 6.2.2.8):

• Push (0b1010) — saves the current values of all global items onto a state stack
• Pop (0b1011) — restores the most recently saved state and pops it from the stack

These tags are used by real devices (for example Wacom digitizers) to temporarily change a subset of global items inside a collection and restore them afterwards.

The library already recognized these tags in print(), but _parse() raised NotImplementedError('Unsupported global tag: 0b1010'), making it impossible to parse such descriptors. This PR implements Push/Pop support in _parse().

Changes

• hid_parser/__init__.py:
  • Track a state stack in _parse() and handle TagGlobal.PUSH / TagGlobal.POP
  • Push saves (usage_page, report_id, report_count, report_size, glob); Pop restores it
  • A Pop without a matching Push raises InvalidReportDescriptor('Pop without a matching Push')
  • Since a Pop can restore a previously saved report_id, report offsets are seeded for that id if missing
• tests/test_parse.py:
  • Regression test: a descriptor that pushes logical min/max, changes them for two axes, then pops and reuses the original global values
  • Test that an unbalanced Pop raises InvalidReportDescriptor

Verification

• Parses the descriptor attached to the original issue (Unsupported global tag: 0b1010 #12), which uses Push at byte 538 and Pop at byte 704 (the 17-item pen collection in report id 6), plus a second Push/Pop pair
• 75 passed (full test suite), mypy clean

Fixes #12