gcc header fixes for Fedora 44

[stevegrubb]

This has 2 commits that fix an include error when compiling with gcc-16 on Fedora 44.

custom loader: include cstdint for uint8_t

customloaderinterface.hpp uses uint8_t in its public method signatures but does
not include the header that declares it. The header therefore compiles only
when another include happens to provide the fixed-width integer definitions,
and fails with current GCC when compiled independently.

Include <cstdint> directly so the public interface is self-contained. This is
an include-only correction with no ABI or behavior change.

and

dags: include cstdint in session_id.hpp

session_id.hpp aliases uint32_t without including <cstdint>. This relies on a
transitive include and fails when the header is compiled with an include order
that does not provide the fixed-width integer declarations.

Include <cstdint> directly so the session ID header owns its dependency. The
alias and its ABI remain unchanged.