fix: fix status code for insufficient fund in new interpreter

[ascandone]

fixes https://formance-team.atlassian.net/browse/EN-703

[coderabbitai]

Walkthrough

Changes refactor error handling for insufficient funds scenarios by embedding numscript.InterpreterError directly in ErrRuntime instead of using a named field, adding a Unwrap() method to support standard error unwrapping semantics, and updating the API to treat numscript.MissingFundsErr identically to ErrInsufficientFunds.

Changes

Cohort / File(s)	Summary
Error Handling Refactoring internal/controller/ledger/errors.go, internal/controller/ledger/numscript_runtime.go, internal/controller/ledger/errors_test.go	Refactored ErrRuntime struct to use anonymous embedded numscript.InterpreterError field (replacing named Inner field), removed explicit Error() method, added Unwrap() method for standard error unwrapping semantics. New test validates that errors.Is() correctly unwraps to underlying MissingFundsErr.
API Insufficient Funds Handling internal/api/v2/controllers_transactions_create.go	Extended error handling in createTransaction to treat numscript.MissingFundsErr as an insufficient funds error, merging it into the same BadRequest path as ErrInsufficientFunds.
API Test Updates test/e2e/api_transactions_create_test.go	Simplified "with insufficient funds" test by removing conditional logic that varied expected error code based on data.numscriptRewrite; now always asserts InsufficientFund error code unconditionally.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Poem

🐰 Errors unwrapped with care divine,
Funds and InterpreterError align,
No Inner names to confuse the way,
Just Unwrap() and errors.Is today!
Tests confirm our logic shines so bright, 🌟

🚥 Pre-merge checks | ✅ 1 | ❌ 2

❌ Failed checks (1 warning, 1 inconclusive)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.
Description check	❓ Inconclusive	No pull request description was provided by the author.	Add a description explaining the rationale for treating numscript.MissingFundsErr as insufficient funds and why the interpreter error structure was refactored.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title accurately describes the main change: fixing status code handling for insufficient funds errors in the new numscript interpreter.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/fix-interpreter-error-code

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[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.49%. Comparing base (7d6d64d) to head (aa79816).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/api/v2/controllers_transactions_create.go	0.00%	0 Missing and 1 partial ⚠️
internal/controller/ledger/errors.go	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1241      +/-   ##
==========================================
- Coverage   74.70%   74.49%   -0.21%     
==========================================
  Files         198      198              
  Lines       10410    10411       +1     
==========================================
- Hits         7777     7756      -21     
- Misses       1508     1513       +5     
- Partials     1125     1142      +17     

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