graph_channels read from memory instead of from DB

[jjyr]

1. Using indexmap struct to store graph channels, thus, we can support paginate in graph_channels.
2. Remove Db access in graph_channels and graph_nodes Rpc
3. Add total_count to result

Drawback:

Since our paginate based on return count, the query result may contains duplicates or missing for multiple pages. It is acceptable since graph_channels is mainly used for statistics, one way to workaround this problems is to set limit large enough to return all channels in once.

Also fixes #534

---

Updated the new commit use BTreeMap to store graph channels and nodes avoid the paginate drawback

[chenyukang]

prefer to use page and per_page as parameters.

[jjyr]

The param is still exposed as last_cursor for the external RPC, so even we change to network_graph.get_channels_with_params(per_page, page * per_page); the extern user feels no difference, and some unneccesary complexity is introduced: need to encode two (page, per_page) instead of one param (after) into last_cursor.

[chenyukang]

and to resolve #534,
please add a total_count field for nodes and channels graph rpc.

[chenyukang]

please do similar refactoring for graph_nodes rpc.

[jjyr]

and to resolve #534, please add a total_count field for nodes and channels graph rpc.

The tricky part is we need to track private_channels_count or public_channels_count, since graph_channels interface only return public channels, updated in the commits

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 53 lines in your changes missing coverage. Please review.
✅ Project coverage is 0.00%. Comparing base (8d98152) to head (e4a2170).
⚠️ Report is 8 commits behind head on develop.

Files with missing lines	Patch %	Lines
crates/fiber-lib/src/fiber/graph.rs	0.00%	28 Missing ⚠️
crates/fiber-lib/src/rpc/graph.rs	0.00%	25 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop    #879   +/-   ##
=======================================
  Coverage     0.00%   0.00%           
=======================================
  Files           61      61           
  Lines        38148   38144    -4     
=======================================
+ Misses       38148   38144    -4     

Flag	Coverage Δ
unittests	0.00% <0.00%> (ø)

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