chore: bump to Solidity 0.8.28 for transient keyword

[BenSparksCode]

Changes:

• Upgrade solc version from 0.8.25 to 0.8.28.
• Remove our manual assembly-based transient storage approach, and instead use the new transient keyword syntax when declaring the variables, introduced in Solidity 0.8.28.
• The initial Solidity version upgrade increases Atlas size by 91 bytes but the transient syntax refactor decreases it by 905 bytes for a net effect of a 814 bytes decrease.

Blockers:

• The new transient keyword currently breaks Foundry's forge fmt. There is an open issue for this: feat(fmt): support transient keyword foundry-rs/foundry#9088