[Exporter] Fix parameter direction and type emission in exportArgument

[p2peek]

This PR fixes parameter emission in the P4HIR → P4 exporter.

Currently, exportArgument(...) only emits annotations and misses:

• parameter direction (in/out/inout)
• parameter type
• parameter name

This change ensures that parameters are printed as valid P4 syntax, e.g.:

in bit<32> arg0

This is a minimal fix toward completing the exporter described in PR #168.

Next steps include:

• extracting actual parameter direction from attributes
• handling parameter names properly
• improving type coverage