feat: Change the order of UNSUFFICIENT_FUNDS and CONFLICT errors

[gfyrag]

Change the order of UNSUFFICIENT_FUNDS and CONFLICT errors

Instead of handling conflict errors at store level (by interpreting error codes from the database server), we check potential reference conflict at core level.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring / Technical debt

[codecov]

Codecov Report

Merging #302 (52a2dce) into main (c510cfa) will decrease coverage by 0.07%.
The diff coverage is 72.72%.

@@            Coverage Diff             @@
##             main     #302      +/-   ##
==========================================
- Coverage   72.05%   71.97%   -0.08%     
==========================================
  Files          82       82              
  Lines        4387     4393       +6     
==========================================
+ Hits         3161     3162       +1     
- Misses        946      952       +6     
+ Partials      280      279       -1     

Impacted Files	Coverage Δ
pkg/ledger/ledger.go	70.94% <0.00%> (-0.97%)	⬇️
pkg/ledger/process.go	84.26% <80.00%> (-0.55%)	⬇️
pkg/storage/storage.go	44.77% <0.00%> (-10.45%)	⬇️
pkg/analytics/segment.go	90.62% <0.00%> (+6.25%)	⬆️

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[antoinegelloz]

lgtm :)