[PR] Stop xsd2inst building digit-facet bounds as strings [p oi-xmlbeans]

pjfanning opened a new pull request, #99:
URL: https://github.com/apache/poi-xmlbeans/pull/99

   Branched from trunk, independent of #98.
   
   ### The bug
   
   `SampleXmlUtil.formatDecimal` derived both digit-facet bounds by building a string and parsing it back — `xsd:totalDigits` as that many nines, `xsd:fractionDigits` as `"0.00...1"`. Both facets are `positiveInteger` with no ceiling of their own, so as soon as a schema asks for more digits than `maxNumberOfCharsForNumbers` allows, `parseAsBigDecimal` rejects the string the method just built:
   
   ```
   IllegalArgumentException: Number has more than 1024 characters
   ```
   
   and `xsd2inst` cannot generate a sample for the schema at all. 5.3.0 used `new BigDecimal(...)` here and was unaffected; the limit arrived in 5.4.0.
   
   A minimal reproducer — nothing else in the schema:
   
   ```xml
   <xs:simpleType name="constrainedDecimal">
     <xs:restriction base="xs:decimal">
       <xs:totalDigits value="2000"/>
     </xs:restriction>
   </xs:simpleType>
   ```
   
   The `fractionDigits` branch fails the same way at 1023.
   
   ### The fix
   
   Compute both values instead of spelling them out:
   
   - `10^totalDigits - 1` for the widest value the facet allows;
   - `BigDecimal.ONE.scaleByPowerOfTen(-fractionDigits)` for the increment, which only sets a scale and expands nothing.
   
   The `totalDigits` bound can only narrow a `min`/`max` that is at least as wide, so it is now computed only when it can actually bind. That is what keeps `10^n` away from a `totalDigits` far larger than any bound the schema declares — the previous code built its string of nines unconditionally, even when no `min` or `max` facet existed for it to constrain.
   
   Behaviour for schemas within the limit is unchanged: `totalDigits` still pulls the seed value down to the widest value it permits.
   
   ### Tests
   
   `testDigitFacetsWiderThanTheNumberLengthLimit` covers both facets past the limit — it fails on trunk with the exception above. `testTotalDigitsStillNarrowsTheBounds` pins the normal case (seed `1000.00`, `totalDigits=3` → `999`) and passes both before and after, so it guards the semantics rather than the fix.
   
   Full suite: 3084 tests, 0 failures.
   
   🤖 Generated with [Claude Code](https://claude.com/claude-code)
   


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