audit: module-by-module code audit fixes and test coverage

Lands the code-audit branches for aacs, css, keys, labels, udf, ifo and
dvd, bdnav/mpls/clpi, disc/bluray, extract, io, scsi, the mkv, mp4,
network and mpg muxers, the audio and video codecs, and CI. Fixes
include MKB and FMTS validation, UDF bounds, IFO fallback to the BUP,
DTS Express framing, MPEG-2 field pairing and mpg re-basing; the rest
pins existing behaviour with tests.

LICENSES/LicenseRef-ISO-dist10.txt

@@ -0,0 +1,11 @@
+ISO/IEC 11172-5 reference software (dist10) -- table data
+
+src/mux/codec/testdata/dist10/alloc_0..3 are the Table 3-B.2a-d bit-allocation
+tables of ISO/IEC 11172-3 Annex B, as shipped in the ISO/MPEG Audio Subgroup
+Software Simulation Group's dist10 reference software (commit ea3c5ee of
+joncampbell123/iso-dist10). They are used here only as test data to check the
+Layer II parser.
+
+Copyright remains with ISO/IEC and the original authors of that software. No
+separate licence text accompanies these files; they are not covered by this
+project's MIT licence, and their terms are those of the dist10 distribution.

LICENSES/MIT.txt

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2026 Matthew Jackson & Contributors
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.