Update to Rust edition 2024

[XSpielinbox]

Partially addresses #37

Backwards-incompatible changes:

• Accept shorter if let temporary scope as discussed in Update dependencies part 1 #38 (comment)
• Accept new macro fragment specifiers - to be discussed
• Accept shorter tail expression temporary scope as discussed in Update dependencies part 1 #38 (comment)
• Only set environment variables on child process to avoid unsafe - as discussed in Update dependencies part 1 #38 (comment)

Builds on #38 , so should be merged afterwards.

[XSpielinbox]

I am unsure how to proceed with the tests as updating them to 2024 would require adding unsafe keywords, though crab-2 forbids the usage of unsafe.

[XSpielinbox]

Closing this as this part was already merged in #40.

I assume that hereby the opt-out of a backwards compatibility for macro fragment specifiers is acknowledged and correct.

The changes to the tests will be done in a new PR.