[AlexeyMatskevich]

With ntex-files, one request can panic the handler: an empty Range header, or a request for a file whose modification time is before 1970 or in year 10000 or later. A suffix range on an empty file overflows an integer subtraction, and Range: bytes=-0 on a non-empty file gets 206, although a zero-length range cannot be satisfied (RFC 9110 section 14.1.2).

What changes

• A file modified before 1970 is served with 200, without ETag and without Last-Modified (test: test_modified_before_epoch).
• With use_etag(false), such a file is served with 200 and without Last-Modified (test: test_modified_before_epoch_without_etag).
• A file modified in year 10000 or later is served with 200 and an ETag, without Last-Modified (test: test_modified_after_year_9999).
• A Range header with no range in it ("", bytes=, bytes=,, bytes= , ,) gets 416 with Content-Range: bytes */<len> (test: test_named_file_empty_range_header).
• bytes=-0 gets 416 with Content-Range: bytes */<len>, also on an empty file (tests: test_named_file_zero_length_suffix_range, test_named_file_range_responses_match_the_selected_bytes).
• HttpRange::parse skips a zero-length suffix range: bytes=-0 yields no range, bytes=-0,2-3 yields 2-3 (test: test_parse).
• A non-zero suffix range such as bytes=-5 on an empty file gets 200 with an empty body and no Content-Range (test: test_named_file_suffix_range_of_empty_file).

Reference

actix-files fixed the same for pre-1970 files in actix/actix-web#3922.

This PR and "NamedFile: support If-Range" touch the same lines of ntex-files/src/lib.rs; the one merged second needs a rebase.