Make troubleshooting/debugging custom accessTokenCallbackClass possible

[divang]

Summary:
This change improves error visibility for custom accessTokenCallbackClass failures by preserving the original exception instead of only its cause.

What changed:
In [SQLServerConnection.java, the thrown SQLServerException now uses e instead of e.getCause().
If callback exception has no cause, the real exception is no longer lost.
If callback exception has a cause, full chained details are still available through the original exception.

Scope:
One file changed.
No functional auth flow change, only better troubleshooting/debugging context.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 60.18%. Comparing base (613e728) to head (99efe2e).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
.../microsoft/sqlserver/jdbc/SQLServerConnection.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2990      +/-   ##
============================================
+ Coverage     59.25%   60.18%   +0.93%     
- Complexity     5046     5140      +94     
============================================
  Files           153      153              
  Lines         36350    36636     +286     
  Branches       6650     6721      +71     
============================================
+ Hits          21538    22051     +513     
+ Misses        11053    10753     -300     
- Partials       3759     3832      +73     

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