gbk.rs and embl.rs should use record.rs as generic type

[LCrossman]

Describe the bug
Currently gbk.rs and embl.rs build separate record types and feature attributes.
These types are essentially identical but are causing problems in downstream applications, hence the
need for a single generic type.

To Reproduce
check the microbiorust-py to see how it requires an InternalRecord enum to deal with two types Gbk::Record and Embl::Record

Expected behavior
Would be better to use the generic types in record.rs

Will require refactoring the gbk.rs and embl.rs to both use record.rs structs