Inconsistent PooledStringBuilder usage

[matt-edmondson]

Should this use PooledStringBuilder like the other function, or should the other function not use it? (or is both valid)

Originally posted by @Damon3000s in #3

[matt-edmondson]

Resolved. Verified against main:

Every operator / overload in Semantics.Paths/Implementations/ now uses PooledStringBuilder.CombinePaths — the raw Path.Combine from the original diff is gone. The only remaining Path.Combine in the implementations is RelativeDirectoryPath.cs:202, inside a Path.GetFullPath normalization, which is a different operation and correctly not pooled.

The file the review comment was on (DirectoryPath.cs) no longer exists. Closing as resolved by subsequent refactoring.