fix(security): Cap untrusted XML/archive reads to bound memory use

[reddraconi]

Two-part fix to TagStudio's XML/archive parsing, delivered as two commits in this PR to address #1341

NOTE: This adds a new dependency, defusedxml.ElementTree and updates the settings UI to include a new Advanced page for these (probably-not-often-touched settings).

1. Swap xml.etree.ElementTree to defusedxml.ElementTree

The stdlib parser is known to be unsafe on untrusted input. It happily expands DTD entities (billion-laughs /
OOM bombs), follows external-entity references that read local files or fetch over HTTP (XXE), and applies
no internal bounds. defusedxml is the recommended drop-in replacement that disables those parser behaviors by default. The Element import is kept from stdlib since defusedxml only ships replacement parsers, not data classes.

We left the legacy core/library/json/library.py xml.etree.ElementTree.parse alone, per
CONTRIBUTING.md guidance. If we need to swap that too, we can.

2. Cap attacker-controlled XML reads

defusedxml only protects the parser. Since there's a handful of calls that happen before the parser can protect us, we'd like to cap those read sizes so a malicious or accidentally-large input doesn't OOM TagStudio

Each path now checks the declared/on-disk size against a byte cap before allocating, raising ValueError with a message that names the exact GlobalSettings field to raise. Caps live as fields on GlobalSettings (canonical defaults in core/constants.py) so users can raise them if they need to:

Setting	Default MiB	Protects
comic_info_max_mb	1	ePub / CB* ComicInfo.xml zip-bomb members
mdp_header_max_mb	1	.mdp (MDIPACK) headers — 32-bit declared length
pdn_header_max_mb	16	.pdn (Paint.NET) headers — 24-bit declared length (matches format ceiling)
dupe_results_max_mb	128	DupeGuru results XML before ET.parse

A new Advanced tab in the settings panel exposes these settings. The renderer paths' ValueError is caught by each method's exception handler and throws as Couldn't render thumbnail error=ValueError log line, so users hitting their cap get useful messages. The dupe registry raises ValueError before ET.parse runs
and bubbles up to the caller in fix_dupe_files.py.

_epub_cover, _mdp_thumb, and _pdn_thumb are no longer @staticmethod because they now read self.driver.settings. All existing call sites already used self.<method>(...), so this should be a no-op for callers.

Tasks Completed

• Platforms Tested:
  • Windows x86
  • Windows ARM
  • macOS x86
  • macOS ARM
  • Linux x86
  • Linux ARM
• Tested For:
  • Basic Functionality
  • PyInstaller Executable
  • pytest: All 231 tests still pass. I added 5 new tests
  • ruff and mypy came back clean.
  • Manual: Opened the new Advanced tab, changed values, save + reloaded to ensure values persisted.