Added length method to bank template

[TSonono]

Does not add startup time but utilizes the startup memoized method _sorted_regs() which means this method should not scale on bank length.

Feel free to close this PR if it doesn't make sense to include this in dml-builtins.

[mandolaerik]

I'm not so concerned about startup time, so memoized would be fine (the static cost is an integer per bank, 8 to 16 bytes in total).

If we are concerned about this cost, then we can make it an optional utility template, like:

template bank_length is bank { shared independent startup memoized method length() -> (uint64) { ...}

so whoever wants it universally can say:

in each bank { is bank_length; }

[mandolaerik]

And as usual, naming is a hard problem. "Length" is somewhat ambiguous (other interpretations: number of regs, sum of reg sizes, difference between lowest and highest offs of a register byte). One option could be to let a method return the highest-offset register object; here, static typing would help eliminating ambiguity in naming.

[mandolaerik]

Also, we need to consider implications for custom implementations of read or write on bank level (such as "simple regs"): Would the existence of a length method mean that read/write overrides are expected to override the length method, to return the largest address with custom behaviour? This is a semantic subtlety that a register return type may help to address: it enforces an unambiguous technical definition; we can only concrete statically declared register objects, so the only sensible return value is the one with the highest offset.

[mandolaerik]

Also, once we agree on a design, we also need to extend the PR with tests and docs.

[syssimics]

Verification #13711935: ✅ pass