max cluster size

[rust-highfive]

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[adamgreig]

Code changes LGTM, what's the use of the max_cluster_size option?

[burrbull]

Code changes LGTM, what's the use of the max_cluster_size option?

When cluster has hole in the end it can be used to extend it size and collect clusters to array:

But you need to check there are no intersections with other registers.

[bors[bot]]

Build succeeded:

• CI
• Rustfmt

[allexoll]

FIY this pr seems to be breaking some things over at lpc-rs/lpc-pac, i still need to investigate what's precisely the issue.