fix: propagate fatal flag across all promise wrapper error paths

[techcodie]

Problem

The promise wrapper layer had two related issues:

1. fatal flag silently dropped in 5 methods

ping(), connect(), prepare(), changeUser() in PromiseConnection and end() in PromisePool all manually copied a fixed set of error properties to localErr before rejecting:

localErr.message = err.message;
localErr.code = err.code;
localErr.errno = err.errno;
localErr.sqlState = err.sqlState;
localErr.sqlMessage = err.sqlMessage;

But err.fatal was never copied. This means promise clients calling these methods could not distinguish fatal errors (e.g. PROTOCOL_CONNECTION_LOST, ECONNREFUSED) from non-fatal ones — a silent behavioral difference from the callback API which always receives fatal.

2. Same copy block duplicated 5 times with no shared abstraction

The repetition is what caused the omission in the first place — there was no single place to add a new property.

Fix

• Extract assignError(localErr, err) helper in make_done_cb.js that copies all error properties including fatal, and export it
• Replace all 5 manual copy blocks in promise/connection.js and promise/pool.js with assignError()
• makeDoneCb itself also uses assignError now for consistency
• Also fixes PromisePool.execute falsy args check (if (args) → if (args !== undefined)) to be consistent with PromisePool.query

Tests

Added test/integration/promise-wrappers/test-promise-connection-error-properties.test.mts covering ping, connect, prepare, and changeUser error propagation.

[codecov]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.58%. Comparing base (3adca00) to head (af1bd14).
⚠️ Report is 37 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/promise/pool.js	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4196      +/-   ##
==========================================
- Coverage   90.64%   90.58%   -0.07%     
==========================================
  Files          86       86              
  Lines       14245    14233      -12     
  Branches     1798     1801       +3     
==========================================
- Hits        12913    12893      -20     
- Misses       1332     1340       +8     

Flag	Coverage Δ
compression-0	90.58% <95.00%> (+0.68%)	⬆️
compression-1	?
static-parser-0	88.11% <95.00%> (-0.23%)	⬇️
static-parser-1	88.99% <95.00%> (-0.07%)	⬇️
tls-0	89.98% <95.00%> (-0.10%)	⬇️
tls-1	90.20% <95.00%> (-0.22%)	⬇️

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