Fix potential hash collisions of traceql StringArray + compare() improvement

[mdisibio]

What this PR does:
This fixes a potential hash collision of StringArray static MapKey. Similar to #5716 (comment) we need to write a separator between values, so that "foo","bar" hashes to a different value than "foobar". Also ports the missing clone of attribute buffers to vparquet5, which was causing panics that caused me to come across this potential hash collision.

A few other changes:

• Removes unnecessary computations of MapKey in the compare() function (we only need to do it once). This is about a 4% improvement in memory.
• Replaces unsafe.Slice/unsafe.StringData with []byte(string) which the compiler can optimize in this case to be zero alloc (confirmed with benchmark).

Which issue(s) this PR fixes:
Fixes n/a

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[stoewer]

We use a similar approach for avoiding hash collisions for the dedicated columns in block_meta.go:L377
I'm not sure what the best method is, but it would be nice to use the same in both places

[mdisibio]

Can you clarify - are you thinking the same seed/separator bytes is enough? Or perhaps shared code. There is a small difference here in that an empty string is ok for attribute values, but not for attribute name in the dedicated columns config.

[stoewer]

Yeah, just suggesting to use the same separator and seed for consistency, not necessarily sharing the same code. It could also be a nice touch to switch from xxhash to fnv (as we don't use xxhash anywhere else).
Mainly suggesting this to make things a bit more consistent. Totally fine if you think it’s out of scope for this PR - don’t want to block it