Bump version to 0.6.0 and document V3 in the README

[tcalmant]

Summary

• Fixed the version inconsistency across the tree: pyproject.toml already said 0.5.0 but most modules still declared version_info = (0, 4, 4); everything (module tuples, :version: docstring fields, pyproject.toml, setup.py) now agrees on 0.6.0
• Documented the biggest gaps in the V3 README section: automatic Java-collection-to-Python type conversion (DefaultObjectTransformer's handled classes), how to catch javaobj.v3.exceptions (JavaObjError, ParseError.offset, UnexpectedOpcodeError, SecurityError, UnsupportedFeatureError), and the parser/writer logger names
• Tightened the top-of-README Features bullet to credit v3 as the full read+write implementation with typed errors and safety limits, not just "marshalling"

Test plan

• Local: ./run_tests_containers.sh 3.13 -> 280 passed, 7 skipped
• ASCII-only grep clean on every added/changed line
• CI (ci-build.yml: lint, full containerized matrix, coverage)

[coveralls]

coverage: 92.232%. remained the same — bump-0.6.0 into master