[PrefixAndSuffix] lets prefix and suffix overlap: [PrefixAndSuffix("\"", "\"")] accepts a lone ", and empty strings always pass #338

What's wrong

PrefixAndSuffixAttribute.ValidateValue (Semantics.Strings/Validation/Attributes/Text/PrefixAndSuffixAttribute.cs:54-71) has two problems.

1. The prefix and suffix can overlap. It checks StartsWith(prefix) and EndsWith(suffix) independently and never requires value.Length >= prefix.Length + suffix.Length. So one character can serve as both the prefix and the suffix.

2. Empty strings always pass. It returns Success for string.IsNullOrEmpty(value). The sibling [StartsWith] (StartsWithAttribute.cs:49-52) and [EndsWith] reject an empty string, and ValidationStrategyTests.EmptyString_WithValidations_HandledCorrectly asserts that rejection for StartsWith.

Reproduced against HEAD 9c64b67:

• A type with [PrefixAndSuffix("\"", "\"")]: Create("\"") succeeds.
• The same type: Create("") succeeds.
• A type with [PrefixAndSuffix("ab", "ba")]: Create("aba") succeeds.

Why it matters

The obvious use of this attribute is a "quoted string" or "delimited token" type. Such a type currently accepts values that don't contain both delimiters, and code downstream that strips prefix.Length and suffix.Length characters will throw ArgumentOutOfRangeException or produce garbage on those values.

Suggested fix

• Fail when value.Length < prefix.Length + suffix.Length.
• Treat an empty string the way [StartsWith]/[EndsWith] do.

Acceptance criteria

• The three inputs above throw ArgumentException from Create.
• The existing PrefixAndSuffix_* tests in AttributeValidationTests.cs (e.g. "PrefixTestSuffix") still pass.