We should specify a minimal viable Rust version

[BinderDavid]

The reason is that I just detected that we cannot compile with rustc 1.79:

error[E0658]: use of unstable library feature 'lazy_cell'
 --> lang/query/src/spans.rs:1:5
  |
1 | use std::sync::LazyLock;
  |     ^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #109736 <https://github.com/rust-lang/rust/issues/109736> for more information

error[E0658]: use of unstable library feature 'lazy_cell'
  --> lang/query/src/spans.rs:51:35
   |
51 |         static EMPTY_INFO_LAPPER: LazyLock<Lapper<u32, Info>> =
   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #109736 <https://github.com/rust-lang/rust/issues/109736> for more information

error[E0658]: use of unstable library feature 'lazy_cell'
  --> lang/query/src/spans.rs:52:13
   |
52 |             LazyLock::new(|| Lapper::new(vec![]));
   |             ^^^^^^^^
   |
   = note: see issue #109736 <https://github.com/rust-lang/rust/issues/109736> for more information

error[E0658]: use of unstable library feature 'lazy_cell'
  --> lang/query/src/spans.rs:57:35
   |
57 |         static EMPTY_ITEM_LAPPER: LazyLock<Lapper<u32, Item>> =
   |                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #109736 <https://github.com/rust-lang/rust/issues/109736> for more information

error[E0658]: use of unstable library feature 'lazy_cell'
  --> lang/query/src/spans.rs:58:13
   |
58 |             LazyLock::new(|| Lapper::new(vec![]));
   |             ^^^^^^^^
   |
   = note: see issue #109736 <https://github.com/rust-lang/rust/issues/109736> for more information

error[E0658]: use of unstable library feature 'lazy_cell'
  --> lang/query/src/spans.rs:52:13
   |
52 |             LazyLock::new(|| Lapper::new(vec![]));
   |             ^^^^^^^^^^^^^
   |
   = note: see issue #109736 <https://github.com/rust-lang/rust/issues/109736> for more information

error[E0658]: use of unstable library feature 'lazy_cell'
  --> lang/query/src/spans.rs:58:13
   |
58 |             LazyLock::new(|| Lapper::new(vec![]));
   |             ^^^^^^^^^^^^^
   |
   = note: see issue #109736 <https://github.com/rust-lang/rust/issues/109736> for more information

[BinderDavid]

cargo-msrv gave the following output:

Check for toolchain '1.80.1-x86_64-unknown-linux-gnu' succeeded
   Finished The MSRV is: 1.80.1