Diff performance improvement by trim lineage

[tzahij]

does two things with lineage scanning of of left(source) branches of diff. in parent-to-child diff

1. removes the end of the left lineage list if it is the same as the right lineage list.
2. remove items from source if they were commited already in the previous lineage list

[codecov-io]

Codecov Report

Merging #921 (e482c6c) into master (825006f) will increase coverage by 0.03%.
The diff coverage is 92.59%.

@@            Coverage Diff             @@
##           master     #921      +/-   ##
==========================================
+ Coverage   45.03%   45.06%   +0.03%     
==========================================
  Files         143      143              
  Lines       11172    11197      +25     
==========================================
+ Hits         5031     5046      +15     
- Misses       5518     5530      +12     
+ Partials      623      621       -2     

Impacted Files	Coverage Δ
catalog/db_diff_scanner.go	79.48% <83.33%> (-1.15%)	⬇️
catalog/db_branch_scanner.go	87.23% <100.00%> (+2.78%)	⬆️
catalog/db_lineage_scanner.go	81.66% <100.00%> (+1.30%)	⬆️
export/export_handler.go	25.64% <0.00%> (-1.03%)	⬇️
auth/setup.go	0.00% <0.00%> (ø)
api/api_controller.go	37.99% <0.00%> (+0.01%)	⬆️
export/tasks_generator.go	76.87% <0.00%> (+0.59%)	⬆️
catalog/cataloger_create_entry.go	100.00% <0.00%> (+5.26%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 825006f...e482c6c. Read the comment docs.

[nopcoder]

expressed my review in PR #928