add the sub-offset operator

[mbKaleb]

Fixes #2335

Added

• sub-offset operator and corresponding documentation.
• corresponding test-cases under bytes,stream, and operators, matching convention over coverage.

Tested

• Complete btest suite: 880 passed, 0 failed, 33 skipped
• New btest coverage: single-offset sub on bytes and stream views with
  boundary cases (0, mid, full length), a const-operand case, and a
  Spicy-syntax assert (tests/hilti/types/bytes/ops.hlt,
  tests/hilti/types/stream/view.hlt, tests/spicy/types/bytes/operators.spicy)

[codspeed-hq]

Merging this PR will not alter performance

✅ 43 untouched benchmarks

---

_{Comparing mbKaleb:topic/mbKaleb/gh-2335-sub-end-offset (07d8e33) with main (9274feb)¹}

Footnotes

1. No successful run was found on main (877b266) during the generation of this report, so 9274feb was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[mbKaleb]

@evantypanski Any thoughts?