Specify minimal rust version

[artlog]

My current system is using a rust version 1.80 which is what my system provides by default. and build fails with it.

Having a minimal version set to 1.85 ( https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#edition-2024 ) should fix it and clearly state from start what version of rust is required / supported ( rust-version = "1.85" ).

Find below the details of my issues

Launching the build will fail with

error[E0599]: no method named `is_multiple_of` found for type `usize` in the current scope
   --> heed/src/envs/env.rs:648:22
    |
648 |         if !new_size.is_multiple_of(page_size::get()) {
    |                      ^^^^^^^^^^^^^^
    |
help: there is a method `next_multiple_of` with a similar name
    |
648 |         if !new_size.next_multiple_of(page_size::get()) {
    |                      ~~~~~~~~~~~~~~~~

For more information about this error, try `rustc --explain E0599`.
error: could not compile `heed` (lib) due to 1 previous error

due to commit fd5ad4a

after fixing it by using previous code it compiles

diff --git a/heed/src/envs/env.rs b/heed/src/envs/env.rs
index ce269db..1d5f1ef 100644
--- a/heed/src/envs/env.rs
+++ b/heed/src/envs/env.rs
@@ -645,7 +645,7 @@ impl<T> Env<T> {
     /// it is okay to call `mdb_env_set_mapsize` for an open environment as long as no transactions are active,
     /// but the library does not check for this condition, so the caller must ensure it explicitly.
     pub unsafe fn resize(&self, new_size: usize) -> Result<()> {
-        if !new_size.is_multiple_of(page_size::get()) {
+        if new_size % page_size::get() != 0 {
             let msg = format!(
                 "map size ({}) must be a multiple of the system page size ({})",
                 new_size,

but i can't run tests

cargo test

Caused by:
  feature `edition2024` is required

  The package requires the Cargo feature called `edition2024`, but that feature is not stabilized in this version of Cargo (1.80.1 (376290515 2024-07-16)).
  Consider trying a more recent nightly release.
  See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#edition-2024 for more information about the status of this feature.

[artlog]

Well it might be that 1.87 is required to get is_multiple_of . Anyway the code should not even try to be built if rust version is not capable of doing it.