Remove `using namespace` in barretenberg header files

[zac-williamson]

program_settings.hpp includes header files that added "using namespace proof_system" and "using namespace barretenberg" declarations. This effects downstream code that relies on these using declarations. This is a big code smell (should really not have using declarations in header files!), however fixing it requires changes in a LOT of files.

We likely have using namespace declarations in header files elsewhere in the codebase that need to be removed.

[maramihali]

this PR https://github.com/AztecProtocol/aztec-packages/pull/2125 removes them

[maramihali]

also it would be better if these issues lived in bberg

[codygunton]

As of 2023-11-21 there are 52 instances 😦