Bump rust-toolchain to rust 1.88

[coolreader18]

Description of Changes

This bumps our rust-toolchain in the file to 1.88, but doesn't bump the MSRV of the bindings crate and its dependents. We could, if we wanted to, but we don't really have an MSRV policy in place and bumps the rust-version in Cargo.toml as well. This is necessary because the v8 crate has a fairly aggressive MSRV and I'd like to not fall too far behind from their latest version, since that's also the version of V8 itself.

This is a precursor to #2839.

API and ABI breaking changes

None

Expected complexity level and risk

2 - rust version changes can cause problems but it's very rare

Testing

Do we want to run any manual testing?

[gefjon]

If we're going to maintain a lower MSRV than we use for development, I'd like to ensure we have CI which runs with that version.

[Centril]

I personally don't see a particularly strong motivation to not bump for bindings and its dependents as well.

[Centril]

I've reviewed @coolreader18's changes. They look good.
I've then changed the Rust version to 1.88 so that we also get let_chains and cargo automatic cache cleaning.
Finally, I've rebased this PR atop of master.
It should be ready for review now.
I'll investigate and fix the internal tests meanwhile.

[Centril]

@cloutiertyler This is ready for review. Private companion is https://github.com/clockworklabs/SpacetimeDBPrivate/pull/1847.

[cloutiertyler]

@Centril I don't believe this is a priority

[Centril]

@cloutiertyler This is a requirement for V8 modules because the v8 dependency uses edition 2024 which does not exist on our version of Rust.

[cloutiertyler]

@Centril Thanks for the clarification!