Release v0.3.0-rc.1

[HCastano]

This is the release candidate for the 0.3.0 release of Core.

This release has a large portion of the non-TDX specific changes outlined in the
Tofino spec. More TDX specific features will come in 0.4.0.

Notably, this includes changes like:

• Fully on-chain registration
• t-of-N signing instead of N-of-N signing
• The addition of the relayer role
• The removal of signing subgroups
• The removal of permissioned access mode

For more details take a look through the CHANGELOG.

[HCastano]

I ran the benchmarks with half the steps and repeat values to save time. Spot checking the bench results it doesn't look like there's much of a difference since the last release.