Refactor head info for better usages for lock

[terencechain]

Refactor chain_info.go and head.go for better lock usages. This follows @farazdagi 's suggestion to apply lock to exported getters and remove lock for internal getters. This eliminated discrepancies where a getter could be missing lock or even dead lock

[nisdas]

Tests fail here

[codecov]

Codecov Report

Merging #7432 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #7432   +/-   ##
=======================================
  Coverage   60.17%   60.17%           
=======================================
  Files         424      424           
  Lines       30451    30451           
=======================================
  Hits        18323    18323           
  Misses       9129     9129           
  Partials     2999     2999           

[farazdagi]

#7429 was accepted w/o checks (probably because of updates to our cluster?). Anyway, go fmt is needed (will push the update now).

[farazdagi]

Issue seems to be more involved (needs mod tidy as well) -- fixing it in #7446