Static map list headers

[tsa96]

Adds a simple header block to static map lists storing

• ident
• length of uncompressed data
• number of maps

Makes C++ allocs faster and simpler.

Checks

• [x] !! DONT IGNORE ME !! I have ran nx run db:create-migration <name> and committed the migration if I've made DB schema changes
• [x] I have included/updated tests where applicable (see Testing)
• [x] I have followed semantic commit messages e.g. feat: Add foo, chore: Update bar, etc...
• [x] My branch has a clear history of changes that can be easy to follow when being reviewed commit-by-commit
• [x] My branch is functionally complete; the only changes to be done will be those potentially requested in code review
• [x] All changes requested in review have been fixuped into my original commits