Unify Cargo.toml format

[koushiro]

• Add taplo config for unifying Cargo.toml format
• Add CI job for checking Cargo.toml format

[gilescope]

FYI I think we are seeing some movement on cargo fmt doing Cargo.tomls finally: rust-lang/rustfmt#5240

[bkchr]

Ty @koushiro, but for now we will not use any external tool to format the toml files. Maybe when it is in rustfmt and stable, we can again speak about this.

[nuke-web3]

#1050 FYI was my take at a uniform convention, not automated though