Shared ownership of NetworkGraph

[jkczyz]

NetworkGraph is owned by NetGraphMsgHandler, but DefaultRouter requires a reference to it. Introduce shared ownership to NetGraphMsgHandler so that both can use the same NetworkGraph. Remove pub visibility of NetGraphMsgHandler's reference now that it doesn't have to be accessed in this manner.

[codecov]

Codecov Report

Merging #1149 (c4d7b9d) into main (c53048a) will increase coverage by 0.24%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1149      +/-   ##
==========================================
+ Coverage   90.21%   90.46%   +0.24%     
==========================================
  Files          70       70              
  Lines       36201    37946    +1745     
==========================================
+ Hits        32660    34327    +1667     
- Misses       3541     3619      +78     

Impacted Files	Coverage Δ
lightning/src/ln/peer_handler.rs	49.66% <ø> (ø)
lightning-background-processor/src/lib.rs	94.95% <100.00%> (-0.03%)	⬇️
lightning-invoice/src/utils.rs	83.48% <100.00%> (+8.95%)	⬆️
lightning/src/ln/channelmanager.rs	87.06% <100.00%> (+3.24%)	⬆️
lightning/src/ln/functional_test_utils.rs	95.13% <100.00%> (-0.01%)	⬇️
lightning/src/ln/functional_tests.rs	97.29% <100.00%> (-0.02%)	⬇️
lightning/src/ln/shutdown_tests.rs	95.87% <100.00%> (-0.02%)	⬇️
lightning/src/routing/network_graph.rs	91.35% <100.00%> (+0.04%)	⬆️
lightning/src/routing/router.rs	91.98% <100.00%> (ø)
... and 3 more

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