Add an overload to xxhash to allow it to take a string constant

[TrentHouliston]

People were using the xxhash function with string constants like xxhash32("Hello"); and it was compiling just fine, and then returning the hash of the first letter.

This adds an overload which makes xxhash32("Hello"); use a template with an N array in order to hash that correctly.

[Copilot]

Pull Request Overview

This PR fixes an issue where calling xxhash functions with string literals (e.g., xxhash32("Hello")) would only hash the first character instead of the entire string. The fix adds template overloads that correctly handle string literals by deducing the array size and excluding the null terminator.

• Added template overloads for both xxhash32 and xxhash64 to handle string literal arrays
• Modified existing template overloads to take references instead of pointers for better type safety
• Added comprehensive tests to verify string literals hash the same as explicit length calls

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/util/serialise/xxhash.hpp	Added string literal template overloads and modified existing templates to use references
tests/tests/util/serialise/xxhash.cpp	Added test scenarios for string literal functionality and updated namespace usage

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