Unfold continuation lines before UTF-8 decode

[peter-boden]

I ran into a manifest where a UTF-8 multibyte sequence was split across mulitple lines, which made the parser crash.

How to reproduce:

podman run --rm quay.io/ovirt/buildcontainer:el10stream bash -lc 'set -e; VERSION=1.9.18; mvn -q dependency:get -Dartifact=org.apache.maven.resolver:maven-resolver-util:${VERSION} -Dmaven.repo.local=/tmp/m2; python3 -c "from javapackages.common.manifest import Manifest; Manifest(\"/tmp/m2/org/apache/maven/resolver/maven-resolver-util/${VERSION}/maven-resolver-util-${VERSION}.jar\")"'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.12/site-packages/javapackages/common/manifest.py", line 48, in __init__
    self._manifest = self._read_manifest()
                     ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/site-packages/javapackages/common/manifest.py", line 70, in _read_manifest
    return content.decode("utf-8")
           ^^^^^^^^^^^^^^^^^^^^^^^
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xc3 in position 1767: invalid continuation byte

Changes introduced:

• process MANIFEST.MF as bytes and join continuation lines before decode
• simplify _normalize_manifest to line split/strip only
• add regression tests