Fix unbound prefix recovery when xmlns:dlna is absent

[sfortis]

Summary

The `strict=False` recovery added in #35 anchored its namespace injection on an existing `xmlns:dlna` declaration. Some real-world devices (JBL Authentics, WiiM/LinkPlay) emit `song:*` tags without declaring `xmlns:dlna`, so the injection was silently skipped and the unbound prefix remained, raising `ParseError` when the path was otherwise supposed to recover.

Observable today: `python-didl-lite==1.5.0` is shipped via `async-upnp-client` into Music Assistant, where JBL Authentics 200 owners still see ~100 `unbound prefix` errors per hour and a broken DLNA state-sync loop (downstream tracking: music-assistant/support#4398).

Fix

Anchor the namespace injection on the DIDL-Lite root opening tag (`<DIDL-Lite`) instead of the optional `xmlns:dlna` declaration. The root element is guaranteed to be present in any valid DIDL-Lite document, so recovery works regardless of which namespace declarations the producer chose to include.

Also batches all missing prefix injections into a single regex substitution rather than looping per-prefix.

Test

Added `test_from_xml_string_unbound_prefix_without_dlna_namespace` that exercises the no-`xmlns:dlna` case. The existing `test_from_xml_string_unbound_prefix` (with `xmlns:dlna` present) still passes.

```
$ python3 -m pytest tests/ -v
...
26 passed in 0.18s
```

`ruff check` clean.

Compatibility

• No behavior change when `strict=True` (recovery gated by `if not strict`).
• No behavior change for XML that did contain `xmlns:dlna` and had unbound prefixes (Handle unbound XML prefixes when strict=False #35 case continues to work).
• Recovers an additional class of input that previously raised.

(Replaces #52, which was accidentally opened from the wrong account.)

[StevenLooman]

Thank you for this PR @sfortis. Apologies for not replying earlier, I must have missed the notification mail.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.82%. Comparing base (bc2d7dc) to head (7792549).
⚠️ Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #53      +/-   ##
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+ Coverage   94.60%   94.82%   +0.21%     
==========================================
  Files           3        3              
  Lines         408      406       -2     
  Branches       46       45       -1     
==========================================
- Hits          386      385       -1     
  Misses         12       12              
+ Partials       10        9       -1     

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[StevenLooman]

Looks good to me. Can you add a Towncrier fragment, as is required for PRs?

[sfortis]

Oops, the fragment was already there but with the wrong name. Fixed.

[StevenLooman]

Thanks!

[StevenLooman]

Do you want a release with this?