smart: read SmartList XML and numeric values as rekordbox does

[vynulldev]

What & why

Two of link-spec's smart-playlist suites crashed before a case ran, so the conformance run skipped them:

• smart-xml-matrix: the import's dump helper parses SmartList XML with Python's strict parser, which raised on a LogicalOperator of wat.
• smart-numeric-boundaries: fractional values in rekordbox's integer columns broke the import's JSON decode.

Both now run and match rekordbox in full. The rules come from link-spec's live results and its notes on rekordbox's parser.

SmartList XML (the dump helper now parses as rekordbox's JUCE parser does)

• Element names match in any case (node, NoDe).
• A closing tag need not match its opening tag.
• A repeated attribute keeps its first value.
• Anything after the first root element is ignored: another root, trailing text, a NUL.
• No rules are read when the XML has a byte-order mark, text before the root, an unclosed element, or a bad entity or attribute.
• Operator and LogicalOperator read as integers, and any LogicalOperator but 2 means all-of.
• Property names match in any case (GENRE works).

Numbers

• Stored values are read as rekordbox reads them, truncated toward zero:

  • BPM as a signed 32-bit integer, and a track whose BPM reads as negative matches no rule;
  • Rating as a signed byte;
  • Length, ReleaseYear and DJPlayCount as small unsigned numbers.

  Real library values are unchanged.

• Rule values read as integers saturating at the int32 limits, so 0.5 is 0 and blank or text is 0.

• The KEY column shows the key alone for a track with zero tempo, and a negative stored tempo by its magnitude, as rekordbox does.

Conformance against rekordbox 7.2.19 goes from 2,764 to 2,942 of 4,250 exact (+178, none lost), and all 287 suites now complete: smart-numeric-boundaries 100/100, smart-xml-matrix 73/73, plus 2 in boundaries, 2 in smart-text-matrix and 1 in smart-rule-matrix.

Tests cover the dump helper's XML and number parsing (run under python3 with sqlcipher3 stubbed), rule integers, signed ratings, negative BPMs and the KEY column label.

Hardware testing

• Tested on: CDJ-2000NXS2

Checklist

• go build ./..., go vet ./..., and go test ./... pass
• gofmt -l . is clean
• New source files carry an SPDX header (GPL-3.0-or-later)
• Tested on real hardware (deck + firmware noted above), or this change doesn't affect deck behaviour
• I agree my contribution is licensed under the project's GPLv3