feedback on mod _cache_information_ instead of CACHE_INFORMATION comment.

[ratmice]

This moves away from a /* CACHE INFORMATION comment. Instead it uses a module and places all the data into constant values. Because the quote crate relies heavily on proc-macro2 token types which lacks a comment token. So it doesn't actually have any representation for comments.

One trick is to the attribute for a doc comment but hide the doc comment in some inner scope.
This is fairly hacky, and inconvenient because rustdoc still will want it to be properly formatted documentation, there is also the possibility that it the tools become smart enough to figure out that these doc strings are unreachable.

fn foo() {
	#[doc = "we can use a doc comment via an attribute in place of a normal comment"]
	mod _ignore_this_module_{}
}

Instead this patch migrates the cache information to a module with constant values. This module is nested within the lrpar_mod! module in order to avoid introducing multiple modules with the cache_information name at top-level when generating multiple parsers.

mod mod_name_y {

   #[allow(unused)]
   mod cache_information {
      ...

      const ERROR_ON_CONFLICTS: bool = true;
      ...
   }
}

[ratmice]

FWIW, been doing local testing using the following patch, this PR is now in a state where PublicIn still works.
But does change the lifetime of that struct. However mod_name is also an &'a str, so it is thankfully not a huge task to add that lifetime.

diff --git a/lrpar/examples/calc_actions/build.rs b/lrpar/examples/calc_actions/build.rs
index c441cb01..e40c6d3b 100644
--- a/lrpar/examples/calc_actions/build.rs
+++ b/lrpar/examples/calc_actions/build.rs
@@ -8,6 +8,7 @@ fn main() {
.rust_edition(lrlex::RustEdition::Rust2021)
.lrpar_config(|ctp| {
ctp.rust_edition(lrpar::RustEdition::Rust2021)

•            .visibility(lrpar::Visibility::PublicIn("crate"))
             .grammar_in_src_dir("calc.y")
             .unwrap()
     })
  

[ratmice]

Just going to go ahead and unmark this as draft since the Visibility now works.
Still happy to change that back to VISIBILITY: &'static str (or anything else for that matter) though if that is preferred.

[ltratt]

Please squash.

[ratmice]

Squashed.