Extend Checkpoints with new sizes and lookup mechanisms

[Amxx]

This PR includes quite a few things:

• Procedural generation of the Checkpoint library, automating the support for various key/value lengths
  • Checkpoints.Checkpoint224: key is uint32 and value is uint224. Usecase: history checkpoints for voting
  • Checkpoints.Checkpoint160: key is uint96 and value is uint160. Usecase: Address sequence (for NFT batch minting)
• For each Checkpoint type, functions availables are:
  • latest()
  • push(key, value)
  • lowerLookup(key): returns the c.value of the first checkpoint for which key <= c.key (or 0 if no such checkpoint exists)
  • upperLookup(key): returns the c.value of the last checkpoint for which key >= c.key (or 0 if no such checkpoint exists)
  • upperLookupRecent(key): same as upperLookup but optimised to look in recent checkpoints.
• Checkpoint.History now uses the Checkpoints.Checkpoint224 structure, with block.number for keys.
  • getAtBlock now uses upperLookupRecent, optimizing for recent value lookup → delayed to further PR

Fixes #3585

PR Checklist

• Tests
• Documentation
• Changelog entry

[Amxx]

Uses ethereum/solidity#9117 (comment) to skip checks

[frangio]

Mostly minor comments. We can merge after this.