Remove the async_signing cfg flag

[TheBlueMatt]

Now that the core features required for async_signing are in
place, we can go ahead and expose it publicly (rather than behind a
a cfg-flag). We still don't have full async support for
get_per_commitment_point, but only one case in channel
reconnection remains. The overall logic may still have some
hiccups, but its been in use in production at a major LDK user for
some time now. Thus, it doesn't really make sense to hide behind a
cfg-flag, even if the feature is only 99% complete. Further, the
new paths exposed are very restricted to signing operations that
run async, so the risk for existing users should be incredibly low.

[TheBlueMatt]

Squash-pushed to address the comments:

$ git diff-tree -U2 6a8bf7694 d2172e389
diff --git a/lightning/src/sign/ecdsa.rs b/lightning/src/sign/ecdsa.rs
index b1bec057d..2f42d3329 100644
--- a/lightning/src/sign/ecdsa.rs
+++ b/lightning/src/sign/ecdsa.rs
@@ -37,6 +37,4 @@ pub trait EcdsaChannelSigner: ChannelSigner {
 	/// Create a signature for a counterparty's commitment transaction and associated HTLC transactions.
 	///
-	/// Note that if signing fails or is rejected, the channel will be force-closed.
-	///
 	/// Policy checks should be implemented in this function, including checking the amount
 	/// sent to us and checking the HTLCs.
@@ -227,5 +225,5 @@ pub trait EcdsaChannelSigner: ChannelSigner {
 	/// signature is computed through [`NodeSigner::sign_gossip_message`].
 	///
-	/// This method is *not* asynchronous, if this fails or is rejected, the channel will not be
+	/// This method is *not* asynchronous. If an `Err` is returned, the channel will not be
 	/// publicly announced and our counterparty may (though likely will not) close the channel on
 	/// us for violating the protocol.
@@ -246,5 +244,5 @@ pub trait EcdsaChannelSigner: ChannelSigner {
 	/// `input_value`: The value of the previous funding transaction output.
 	///
-	/// THis method is *not* asynchronous. If an `Err` is returned, the channel will be immediately
+	/// This method is *not* asynchronous. If an `Err` is returned, the channel will be immediately
 	/// closed.
 	fn sign_splicing_funding_input(

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.43%. Comparing base (d1e94bd) to head (d2172e3).
Report is 42 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3486      +/-   ##
==========================================
- Coverage   89.70%   89.43%   -0.28%     
==========================================
  Files         130      150      +20     
  Lines      107882   117600    +9718     
  Branches   107882   117600    +9718     
==========================================
+ Hits        96778   105174    +8396     
- Misses       8695     9966    +1271     
- Partials     2409     2460      +51     

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[valentinewallace]

I noticed that ChannelManager::signer_unblocked docs sound like it needs to be called whenever any of these methods errors. It's clear in these docs which signer_unblocked method needs to be called, but there it could be clearer and {Chain,Channel}Monitor::signer_unblocked could also benefit from referencing these docs IMO. Doesn't need to happen in this PR though.