exclude: review-driven cleanup, stdin support and memcheck

[jqnatividad]

Summary

Continues the recent sweep of review-driven cleanups on individual qsv subcommands (slice #3748, fetch/fetchpost #3747, schema #3746, frequency #3745).

• Strip dead ValueIndex machinery. The random-access row-position index (idx, num_rows, byte-offset buffer, Indexed::open, the header-vs-no-headers seek branch, the unused Vec<usize> row tracker) was decorated #[allow(dead_code)] and never read by exclude. Collapsed to a plain HashSet<Vec<ByteString>> and dropped the byteorder/crate::index::Indexed deps from this file. Also removes the only .unwrap() in the hot path (row.position().unwrap()).
• Stdin support. Switched both inputs from reader_file() to reader_file_stdin() so either <input1> or <input2> can be -. Errors out cleanly if both are stdin.
• --memcheck flag. <input2> is fully loaded into memory; added a --memcheck flag and util::mem_file_check guard, matching the dedup convention.
• Polish. Named VALUE_SET_INITIAL_CAPACITY const, get_row_key helper used at both sites, read_byte_record loop replaces the #[allow(unused_assignments)] pattern, match block collapsed to if matched == invert.
• Tests. Added column-range, tab delimiter, stdin, both-stdin error, and mismatched-column-count coverage (6 → 11 tests).

Test plan

• cargo build --locked --bin qsv -F all_features
• cargo t exclude -F all_features (11/11 pass)
• cargo clippy --bin qsv -F all_features -- -D warnings
• qsv --generate-help-md regenerated docs/help/exclude.md
• Manual: printf 'id\n1\n2\n3\n' | qsv exclude id - id <(printf 'id\n2\n') prints id=1,3

🤖 Generated with Claude Code

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 14 complexity

Metric	Results
Complexity	14

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[Copilot]

Pull request overview

This PR continues the review-driven cleanup sweep by refactoring the exclude subcommand to simplify its internal matching/indexing approach, add stdin support, and introduce an optional memory guard for the in-memory side of the operation.

Changes:

• Removed the unused random-access/indexing machinery in exclude, replacing it with a straightforward in-memory value set for <input2>.
• Added stdin support (-) for either <input1> or <input2> (but not both), plus a --memcheck guard for <input2> when it is a file.
• Expanded exclude test coverage for column ranges, tab delimiters, stdin usage, both-stdin erroring, and mismatched selection sizes; regenerated help markdown.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/cmd/exclude.rs	Simplifies exclusion logic to a HashSet-based value set, adds stdin support and a --memcheck option, and updates CLI help text.
tests/test_exclude.rs	Adds regression/feature tests for column-range selection, tab delimiter handling, stdin input, and new error cases.
docs/help/exclude.md	Regenerates user-facing help to document stdin usage and the new --memcheck flag.