Simplify regex in MappingUtils.evaluateFileNameMapping

[elharo]

Summary

Remove the unnecessary empty capture group and __artifact prefix trick from the RegexBasedInterpolator pattern in MappingUtils.evaluateFileNameMapping.

Problem

The previous regex used startRegex='\\@\\{(' and endRegex=')?([^}]+)\\}@' with thisPrefixPattern='__artifact', creating the pattern:

\@\{(__artifact)?([^}]+)\}@

This contained an unused optional group (__artifact)? that served no real purpose -- the __artifact string was a dummy prefix intended to be filtered out by the optional group, but since the custom prefix/suffix already delimit @{...}@ expressions, the prefix filtering is redundant.

Fix

The new approach uses an empty startRegex with the full capture pattern in endRegex and passes null for thisPrefixPattern:

RegexBasedInterpolator interpolator = new RegexBasedInterpolator("", "\\@\\{([^}]+)\\}@");
return interpolator.interpolate(expression, (String) null);

This produces the simpler pattern \@\{([^}]+)\}@ with the key captured directly in group 1.

Verification

All existing tests pass without modification:

• completeMapping
• noVersionMapping
• mappingWithGroupId
• mappingWithClassifier
• mappingWithNullClassifier
• mappingWithOptionalClassifier (MWAR-212)

Closes #67