PDM lock files represent the same logical package as multiple [[package]] entries when extras are used in the dependency tree. This differs from Poetry, which uses a single entry with conditional markers.

For example, when a project depends on coverage[toml], PDM generates:

[[package]]
name = "coverage"
version = "7.4.1"
# base package

[[package]]
name = "coverage"
version = "7.4.1"
extras = ["toml"]
dependencies = [
    "coverage==7.4.1",
    "tomli; python_full_version <= \"3.11.0a6\"",
]

Similarly, if different packages require different extras combinations (e.g., package[redis] and package[postgres]), PDM creates separate entries for each.

The fix in this PR merges pkg.Package instances for the same high-level/logical package together. Variants are captured in the metadata.

Changes

• removed custom buildPdmRelationships() function and used the standard dependency specifier pattern used in other catalogers
• added support for detecting and processing extras (added PythonPdmLockExtraVariant struct to represent extras combinations)
• preserves full dependency strings including environment markers (e.g., ; python_version < "3").... these were being stripped
• filters self-references in extras dependencies (e.g., coverage[toml] depending on coverage==7.4.1)

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• I have added unit tests that cover changed behavior
• I have tested my code in common scenarios and confirmed there are no regressions
• I have added comments to my code, particularly in hard-to-understand sections