NBK-183: remove dead DDSQL interval and offset flags

[nmuldavin]

Linear

NBK-183 — https://linear.app/datadoghq/issue/NBK-183/pup-remove-dead-ddsql-interval-and-offset-flags

Scope

• Remove --interval and --offset from DDSQL table parsing, dispatch, implementation signatures, help, and documentation.
• Help text directs clients towards SQL LIMIT, OFFSET and --from, --to time controls instead
• Help text specifies use of --limit param only to extend row limit
• Row limit default set to 5k, matching public API

Acceptance

• pup ddsql table --offset 5 and --interval 60000 exit with an unknown-argument error.
• Neither removed flag appears in DDSQL table help, DDSQL long help, or docs/COMMANDS.md.
• Help and docs name OFFSET n LIMIT m, --from/--to, and per-source table-function timestamps, without recommending a WHERE time filter for granularity.
• Ordered live DDSQL queries with OFFSET 0 LIMIT 3 and OFFSET 5 LIMIT 3 return distinct three-row pages.
• --limit still parses and is covered mapping to row_limit in the public v2 request.
• --limit default matches the public API's default (5000)

Validation

• cargo test test_ddsql_ — 9 focused DDSQL tests passed on latest main.
• cargo test -- --test-threads=1 — all 1,906 tests passed.
• cargo clippy -- -D warnings — passed.
• cargo fmt -- --check — passed.
• Branch binary smoke test — removed flags both exited 2 with unexpected argument.
• Branch binary live read-only DDSQL probe — ORDER BY ts OFFSET 0 LIMIT 3 and OFFSET 5 LIMIT 3 each returned three rows with different timestamps.
• Two independent fresh-context reviews — no findings.

Not run / automation gaps

• cargo audit — cargo-audit is not installed locally. This change adds or updates no dependencies.
• The default parallel cargo test run hit six process-global mock-environment races against unused.local; the serial full suite passed. No affected source or test was changed in response.