Move keysinterface.rs to a directory-level module called sign

[arik-so]

Fixes #2157.

[codecov-commenter]

Codecov Report

Patch coverage: 66.66% and project coverage change: -0.01 ⚠️

Comparison is base (ec3de62) 91.62% compared to head (6cb9919) 91.61%.

📣 This organization is not using Codecov’s GitHub App Integration. We recommend you install it so Codecov can continue to function properly for your repositories. Learn more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2246      +/-   ##
==========================================
- Coverage   91.62%   91.61%   -0.01%     
==========================================
  Files         104      104              
  Lines       51949    51949              
  Branches    51949    51949              
==========================================
- Hits        47597    47592       -5     
- Misses       4352     4357       +5     

Impacted Files	Coverage Δ
lightning-background-processor/src/lib.rs	83.18% <ø> (ø)
lightning-block-sync/src/init.rs	92.57% <ø> (ø)
lightning-invoice/src/payment.rs	89.11% <ø> (ø)
lightning-invoice/src/utils.rs	97.17% <ø> (ø)
lightning-persister/src/lib.rs	89.25% <ø> (ø)
lightning/src/blinded_path/mod.rs	93.18% <ø> (ø)
lightning/src/chain/chainmonitor.rs	94.65% <ø> (ø)
lightning/src/chain/channelmonitor.rs	94.82% <ø> (ø)
lightning/src/chain/mod.rs	80.95% <ø> (ø)
lightning/src/chain/onchaintx.rs	92.54% <ø> (-0.35%)	⬇️
... and 37 more

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[TheBlueMatt]

LGTM, why is this a draft?

[arik-so]

I wasn't sure if people would want me to add some more subdivision in this PR, like the entropy source, for example. I'm undrafting it.

[TheBlueMatt]

Two PRs better than one :)

[TheBlueMatt]

Will let @jkczyz comment as he'd previously proposed other naming at #2159 (comment)

[TheBlueMatt]

This should be tagged as closing #2157

[arik-so]

@jkczyz and I also discussed this out of band in Austin.