chore: clean up 26 TODOs in column_store and pipeline modules

[devin-ai-integration]

Reference Issues/PRs

N/A — GitHub issues are disabled on this fork. TODO items reference Monday tickets where applicable.

What does this implement or fix?

Resolves 26 TODO comments across 15 files in the column_store (18 TODOs) and pipeline (8 TODOs) modules by categorizing each into structured annotations:

Approach per TODO type:

• Obsolete TODOs → Removed (e.g., ensure_norm_meta in frame_utils.cpp — function doesn't exist in the codebase)
• Dead code → Removed (commented-out test code in test_column.cpp)
• Feature/optimization TODOs → Converted to structured OPTIM: or FIXME: comments with clear descriptions
• Monday ticket references → Preserved for traceability

Column store files (18 TODOs across 9 files):

File	TODOs	Action
chunked_buffer.hpp	4	Conservative: all converted to structured OPTIM/FIXME comments, no behavior changes
column.cpp	3	Reclassified (cache rs_index, string row_count verification, sparse split)
memory_segment_impl.cpp	3	Reclassified (O(1) bitset check, protected accessor, protobuf sparsity)
column_algorithms.hpp	2	Reclassified (random access iterator, bitset traversal)
column_utils.cpp	2	Consolidated duplicate Pandas 2.0 datetime comments
column.hpp	1	Reclassified (cross-type search_sorted)
memory_segment_impl.hpp	1	Reclassified (protobuf sparsity flag)
segment_utils.cpp	1	Reclassified (stats-based unique count)
test/test_column.cpp	1	Removed dead commented-out test code, kept clean OPTIM note

Pipeline files (8 TODOs across 6 files):

File	TODOs	Action
column_stats_dispatch.cpp	2	Reclassified (bool support, remaining boolean cases)
frame_utils.cpp	2	Reclassified uint64_t type change; removed obsolete ensure_norm_meta
frame_utils.hpp	1	Reclassified (BYTES_DYNAMIC64 handling)
frame_slice_map.hpp	1	Reclassified (string type handler migration)
index_writer.hpp	1	Reclassified (class rename suggestion)
pipeline_utils.hpp	1	Reclassified (arrow output format)

Any other comments?

• No behavior changes — this is a comment-only cleanup. All functional code is unchanged.
• Conservative with chunked_buffer.hpp — as a core data structure, all 4 TODOs were converted to structured comments rather than implementing any fixes.
• Lint passes (clang-format check clean).

Checklist

Checklist for code changes...

• Have you updated the relevant docstrings, documentation and copyright notice?
• Is this contribution tested against all ArcticDB's features?
• Do all exceptions introduced raise appropriate error messages?
• Are API changes highlighted in the PR description?
• Is the PR labelled as enhancement or bug so it appears in autogenerated release notes?

No API changes, no new exceptions, no behavior changes — comment-only cleanup.

Link to Devin session: https://app.devin.ai/sessions/b69344ef00a14b609e13f521056d0859
Requested by: @chrischappell-cog

---

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.