fix(entity): reject empty and malformed entity tag ranges (#145, #148)

[CyberneticX-Tech]

According to RFC 7232 Sections 3.1 & 3.2 (and RFC 9110 Section 13.1), If-Match and If-None-Match are defined as * or 1#entity-tag (at least one entity tag).

Currently, EntityTagRange::try_from_values succeeds when given an empty iterator or empty values (e.g. IfMatch::decode(&mut [].into_iter()) or &HeaderValue::from_static("")), returning an empty EntityTagRange::Tags(flat) that contains no valid entity tags.

This change:

1. Validates that values is non-empty before decoding.
2. Checks that if the value is not *, it contains at least one entity tag and all tags parse successfully via EntityTag::parse.
3. Adds decode unit tests for both IfMatch and IfNoneMatch covering empty iterators, empty values, whitespace, invalid tag formats, *, and valid tag lists.

Closes #145
Closes #148