fix: support both _init_elsdk.py and _elsdk_.py (irispython >= 3.4 rename)

[isc-tdyar]

Problem

_get_iris_dbapi_module() in iris_vector_rag/common/iris_dbapi_connector.py only searches for _init_elsdk.py. In intersystems-irispython >= 3.4 the file was renamed to _elsdk_.py. The search loop finds nothing, connect() is never injected, and all DBAPI connections return None.

Workaround (users can apply themselves):

IRIS_PKG=$(python3 -c "import iris; import os; print(os.path.dirname(iris.__file__))")
ln -sf "$IRIS_PKG/_elsdk_.py" "$IRIS_PKG/_init_elsdk.py"

Fix

Add an inner loop that checks both filenames for each search directory:

for candidate_name in ('_init_elsdk.py', '_elsdk_.py'):
    candidate_path = os_mod.path.join(search_dir, candidate_name)
    if os_mod.path.exists(candidate_path):
        init_elsdk_path = candidate_path

One inner for loop, no new logic. Backward-compatible — old packages (with _init_elsdk.py) still work; new packages (with _elsdk_.py) now work too.

Testing

Verified against intersystems-irispython 5.3.1 (which ships _elsdk_.py) on macOS ARM64 and Ubuntu ARM64.