How do we keep track of changes waiting on a higher MSRV?

[EliahKagan]

Some changes cannot be made now but are planned for when the minimum supported Rust version is high enough to support them (either to make a language or library feature available, or for it to be stabilized). This includes at least the following:

• Drop once_cell #1518
• use NotADirectory io error kind where appropriate #1775

There may be others such closed PRs. There are also various MSRV-related TODO comments, such as:

gitoxide/gix-fs/src/lib.rs

Lines 90 to 95 in 8df0db2

	/// Return `true` if `err` indicates that the entry doesn't exist on disk. `raw` is used as well
	/// for additional checks while the variants are outside the MSRV.
	pub fn is_not_found(err: ErrorKind, raw_err: Option<i32>) -> bool {
	// TODO: use variant once MSRV is 1.83
	err == ErrorKind::NotFound || raw_err == Some(20)
	}

gitoxide/gix-merge/src/blob/builtin_driver/text/mod.rs

Lines 106 to 108 in 8df0db2

	/// The amount of conflict marker characters to print by default.
	// TODO: use NonZeroU8::new().unwrap() here once the MSRV supports it.
	pub const DEFAULT_MARKER_SIZE: u8 = 7;

How are, or should, such plans be tracked? Comments are one way of tracking them, of course, but there does not always seem to be such a comment, and sometimes a change would touch several places in the code (such as using LazyLock) such that it is no clear ideal place to have a comment about it.