chore: bump version to 4.0.0rc2

Pulls in PR #158 (init err_handler.ele_node_added) — fix for the
AttributeError that surfaced under production traffic against
4.0.0rc1 when apply_segment_errors emits seg-level errors that skip
add_ele.

Pre-flight verification on this branch:
- pytest: 538/538 green (535 + 3 new from #158)
- mypy --strict: clean across 83 source files
- ruff format + check: clean
- tools/check_maps.py: 32 maps clean
- tools/test_install.py: post-packaging smoke suite green

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: azoner

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "pyx12"
-version = "4.0.0rc1"
+version = "4.0.0rc2"
 description = "HIPAA X12 validator, parser and converter"
 readme = "README.md"
 requires-python = ">=3.11"

pyx12/version.py

@@ -1 +1 @@
-__version__ = "4.0.0rc1"
+__version__ = "4.0.0rc2"