Linting and RTF encoding errors from #128

[nanxstats]

Two issues from the changes made in #128

Running ruff check:

F841 Local variable `cell_count` is assigned to but never used
   --> tests/test_encoding_engine.py:210:9
    |
208 |         # Each data row should have 2 cells, not 3
209 |         cell_pattern = r"\\cell"
210 |         cell_count = result.count(cell_pattern)
    |         ^^^^^^^^^^
211 |
212 |         # We have 4 data rows + headers, so we expect cells for 2 columns
    |
help: Remove assignment to unused variable `cell_count`

Running mkdocs serve or sh scripts/check_rtf.sh:

advanced-group-by-group-newpage.rtf
WARNING -  markdown_exec: Execution of python code block exited with errors

           Code block is:

             # Create treatment-separated document with group_by within each page
             # Filter data to have multiple treatment groups
             ae_with_treatments = (
                 ae_t1.filter(pl.col("TRTA").is_in(["Placebo", "Xanomeline High Dose"]))
                 .select(["TRTA", "USUBJID", "ASTDY", "AEDECD1", "AESEV"])
                 .head(40)
                 .sort(["TRTA", "USUBJID", "ASTDY"])
             )

             doc_treatment_separated = rtf.RTFDocument(
                 df=ae_with_treatments,
                 rtf_title=rtf.RTFTitle(
                     text=[
                         "Adverse Events Listing",
                         "Example 5: group_by + new_page (Treatment Separation)",
                     ],
                     text_convert=False,
                 ),
                 rtf_column_header=rtf.RTFColumnHeader(
                     text=["Treatment", "Subject ID", "Study Day", "Adverse Event",
           "Severity"],
                     text_format="b",
                     text_justification=["l", "l", "c", "l", "c"],
                 ),
                 rtf_body=rtf.RTFBody(
                     page_by=["TRTA"],  # Separate pages by treatment
                     new_page=True,  # Force new page for each treatment
                     group_by=[
                         "TRTA",
                         "USUBJID",
                         "ASTDY",
                     ],  # Suppress duplicates within each treatment page
                     col_rel_width=[2, 3, 1, 4, 2],
                     text_justification=["l", "l", "c", "l", "c"],
                     pageby_header=True,  # Repeat headers on each treatment page
                 ),
                 rtf_footnote=rtf.RTFFootnote(
                     text=[
                         "Example of group_by + new_page combination:",
                         "- Each treatment group gets its own page(s) (new_page=True)",
                         "- Within each treatment, USUBJID and ASTDY are suppressed when
           duplicate (group_by)",
                         "- Headers are repeated on each treatment page
           (pageby_header=True)",
                     ],
                     text_convert=False,
                 ),
             )

             # Generate the RTF file
             doc_treatment_separated.write_rtf("advanced-group-by-group-newpage.rtf")

           Output is:

             Traceback (most recent call last):
               File
           "/Users/nanx/rtflite/.venv/lib/python3.14/site-packages/markdown_exec/_internal/formatters/python.py",
           line 71, in _run_python
                 exec_python(code, code_block_id, exec_globals)
                 ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
               File
           "/Users/nanx/rtflite/.venv/lib/python3.14/site-packages/markdown_exec/_internal/formatters/_exec_python.py",
           line 8, in exec_python
                 exec(compiled, exec_globals)  # noqa: S102
                 ~~~~^^^^^^^^^^^^^^^^^^^^^^^^
               File "<code block: session default; n9>", line 48, in <module>
                 doc_treatment_separated.write_rtf("advanced-group-by-group-newpage.rtf")
                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
               File "/Users/nanx/rtflite/src/rtflite/encode.py", line 438, in write_rtf
                 rtf_code = self.rtf_encode()
               File "/Users/nanx/rtflite/src/rtflite/encode.py", line 415, in rtf_encode
                 return engine.encode_document(self)
                        ~~~~~~~~~~~~~~~~~~~~~~^^^^^^
               File "/Users/nanx/rtflite/src/rtflite/encoding/engine.py", line 36, in
           encode_document
                 return strategy.encode(document)
                        ~~~~~~~~~~~~~~~^^^^^^^^^^
               File "/Users/nanx/rtflite/src/rtflite/encoding/strategies.py", line 790, in
           encode
                 suppressed_df = grouping_service.enhance_group_by(full_df, group_by_param)
               File "/Users/nanx/rtflite/src/rtflite/services/grouping_service.py", line
           44, in enhance_group_by
                 raise ValueError(f"group_by columns not found in DataFrame:
           {missing_cols}")
             ValueError: group_by columns not found in DataFrame: ['TRTA']

[nanxstats]

Fixed by #134