pytket v1.21.0 release candidate 0

What's Changed

• Bump circuit renderer version to 0.7 by @DNA386 in #1063
• Feature/symengine 0.11.1 by @cqc-alec in #1064
• Use github-hosted runners for MacOS arm64 builds by @cqc-alec in #1065
• Bugfix/bind sympy.exp() by @yao-cqc in #1069
• Ensure determinate order of Phase commands by @cqc-alec in #1074
• Fix typo in release workflow. by @cqc-alec in #1076
• Improve typing by @trvto in #1072
• implement register iteration by @trvto in #1075
• add more wasm examples and clean up checks by @cqc-melf in #1070

Full Changelog: v1.20.2rc0...v1.21.0rc0