Honor suffix byte ranges larger than the response body

[Mirochill]

A request such as Range: bytes=-100 for a four-byte representation currently produces a 416 response. RFC 9110 section 14.1.2 specifies that a suffix longer than the selected representation selects the entire representation.

Clamp the resolved suffix start to zero for non-empty representations. Update the existing contradictory unsatisfiable assertion, cover suffix lengths equal to and larger than the representation, and test a complete conditional response including its status, Content-Range, Content-Length and body. Add an unreleased changelog entry.

Specification: https://www.rfc-editor.org/rfc/rfc9110.html#section-14.1.2

Validation:

• Before the fix: three new regressions fail (two oversized range cases and the 416 response).
• Python 3.14.8: the complete suite passes, 2,402 passed and one expected failure.
• Statement coverage is 100% for all 5,123 statements, including the byte-range module.
• Repository-wide Black (44 files) and isort checks pass, as do check-manifest, source/wheel builds, twine check and the documentation build with warnings treated as errors; git diff --check passes.

AI assistance: this patch and its tests were developed with OpenAI Codex.

Existing behavior for empty representations and zero-length suffixes is outside this fix.