Honor --no-headers for --fmt and --table output (#566)

[JOhnsonKC201]

Refs #566.

Problem

--no-headers was only honored for --csv/--tsv output. For the tabulate formats (--fmt ... and -t/--table) the flag was silently ignored, so the column-name header row was always printed:

$ sqlite-utils query library.db 'select asin from audible' --fmt plain --no-headers
asin        # <- should not be here
0062804006
0062891421

The two tabulate.tabulate(...) call sites (the query/memory output and the rows/tables output) always passed headers=headers regardless of the flag.

Fix

Both call sites now pass headers=() if no_headers else headers. tabulate renders headerless output cleanly for every format (plain, simple, github, grid, rst, …), so --no-headers now works consistently across CSV, TSV and all --fmt/--table formats. Default output (headers shown) is unchanged, and the CSV/TSV path is untouched.

$ sqlite-utils query library.db 'select asin from audible' --fmt plain --no-headers
0062804006
0062891421

I went with making the flag do what its name says (rather than raising an error on --fmt + --no-headers) because tabulate supports headerless rendering for all formats and this matches the documented purpose of the flag — and the use case in the issue (piping a single column into xargs/unix tools) is a legitimate one.

The --no-headers help text previously said "Omit CSV headers"; it now reads "Omit headers from CSV/TSV and table/--fmt output", and docs/cli-reference.rst is regenerated via cog to match.

Tests

Added test_output_table_no_headers, parametrized over --fmt simple, -t and --fmt github, asserting the header row is omitted (and the data preserved) for both the query and rows commands.

• Full suite: 1042 passed, 17 skipped locally.
• black . --check, cog --check README.md docs/*.rst and codespell all pass.

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📚 Documentation preview 📚: https://sqlite-utils--751.org.readthedocs.build/en/751/