v0.8.64

ApproxFunBase v0.8.64

Diff since v0.8.63

Merged pull requests:

• Bump actions/cache from 3 to 4 (#624) (@dependabot[bot])
• Use mutable copies in transform/itransform (#625) (@jishnub)
• Backport: Use mutable copies in transform/itransform (#626) (@jishnub)
• Convert to float in transform/itransform (#627) (@jishnub)