feat: add syntax macro + maintenance

[alejandro-vaz]

this PR adds a small private procedural macro that allows for syntax inserting like the add-syntax::prepend macro does

it reduces code bloat by conditionally inserting syntax where needed, ensuring the codebase is DRY. unblocks #754 and #762

other maintenance changes

1. upgrades callgrind from 0.14 to 0.16
2. refactors workspace TOML variables for clarity and consistency
3. orders feature dependencies on alphabetical order
4. explicitly notes in the readme that proptest requires std
5. adds missing metadata to the fuzzer
6. compacts one block with the new macro on lib.rs

[Chandana5599]

Thanks for the suggestion! I’ve reviewed PR #764 and understand the simplification. I’ll update PR #762 to use the conditional may_dangle attribute and the syntax macro once the macro is available in the base branch.