fix: fully qualify usages of concat to protect against ADL (#4955)

* Call concat with proper namespace in cast.h

* Apply suggestions from code review

* tests: add test for ADL on concat

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

* fix: fully qualify all usages of concat

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

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Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: Henry Schreiner <HenrySchreinerIII@gmail.com>