Move the public channel state API into a new module

[TheBlueMatt]

Our "what is the channel's current state" structs have slowly
grown to be rather nontrivial, and now include eight structs with
many fields. Thus, it makes sense to pull them out of
ln::channelmanager and into their own module.

This also makes things easier for the C bindings which don't
support pub use from a private module.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.64865% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.51%. Comparing base (7326334) to head (83112b2).
Report is 5 commits behind head on main.

❗ Current head 83112b2 differs from pull request most recent head 2d6d5cc

Please upload reports for the commit 2d6d5cc to get more accurate results.

Files	Patch %	Lines
lightning/src/routing/router.rs	80.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3089      +/-   ##
==========================================
+ Coverage   89.90%   90.51%   +0.61%     
==========================================
  Files         117      118       +1     
  Lines       97415   101836    +4421     
  Branches    97415   101836    +4421     
==========================================
+ Hits        87581    92179    +4598     
+ Misses       7272     7185      -87     
+ Partials     2562     2472      -90     

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[dunxen]

LGTM but just need to fix the fuzz imports in the final commit as well.

[tnull]

LGTM, but wondering if the last commit should get squashed into the first one?

[TheBlueMatt]

Fixed the fuzz failures.

As long as they aren't touching the same lines...more commits better 🤷‍♂️?

[TheBlueMatt]

Fixed dumb sorting:

$ git diff-tree -U1 83112b2de 2d6d5cc86
diff --git a/lightning/src/ln/mod.rs b/lightning/src/ln/mod.rs
index f2af986fa..888044b7a 100644
--- a/lightning/src/ln/mod.rs
+++ b/lightning/src/ln/mod.rs
@@ -18,2 +18,3 @@ pub mod channelmanager;
 pub mod channel_keys;
+pub mod channel_state;
 pub mod inbound_payment;
@@ -33,4 +34,2 @@ pub(crate) mod peer_channel_encryptor;

-pub mod channel_state;
-
 #[cfg(fuzzing)]

[tnull]

Going ahead and merging this