[Feature] Evaluate an embedded DB like HSQL or H2 instead of data structures

[tomaytotomato]

Discussed in #32

^{Originally posted by jottinger August 13, 2024}
The biggest concern with the data structures is that they're internal and manual - a database would be able to do what the data structures do far better. But a database: which one? H2? HSQLDB? Those would be the best candidates, but they're very common - which means you might conflict with someone else's dependency.