[Enhancement] Custom converters registered with supportExcelTypeKey() == null never apply when reading #1085

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Fesod version

2.0.2-incubating (the code path is unchanged on current main)

JDK version

1.8

Operating system

Windows 10

Minimal reproduce step

Register a custom converter whose supportExcelTypeKey() returns null (the wildcard
contract: match every cell data type), then read a file whose cells are plain strings:

public static class BooleanYesNoConverter implements Converter<Boolean> {

    @Override
    public Class<?> supportJavaTypeKey() {
        return Boolean.class;
    }

    @Override
    public CellDataTypeEnum supportExcelTypeKey() {
        return null; // wildcard: match every cell type
    }

    @Override
    public Boolean convertToJavaData(ReadCellData<?> cellData, ExcelContentProperty contentProperty,
            GlobalConfiguration globalConfiguration) {
        return "yes".equalsIgnoreCase(cellData.getStringValue());
    }
}

// the file contains STRING cells "yes" and "no"
FesodSheet.read(file, BooleanReadData.class, listener)
        .registerConverter(new BooleanYesNoConverter())
        .sheet()
        .doReadSync();

Current behavior

The wildcard converter is silently ignored on the read path. ConverterUtils#convertToJavaObject
looks the converter up with the concrete cell type key (Boolean, STRING); a converter registered
under the wildcard key (Boolean, null) never matches, so the built-in BooleanStringConverter
takes over and Boolean.valueOf("yes") returns false — the row is silently read as
flag = false, no warning is logged.

Two more notes:

• Control case: registering the identical converter with an explicit
  CellDataTypeEnum.STRING key works on read — only the wildcard registration is broken.
• For types/classes without any built-in concrete-key converter, the read fails with
  ExcelDataConvertException: Converter not found instead.

The same registration works on the write path for xlsx, where the lookup key is
(Boolean, null) — so read and write disagree about the wildcard contract. See #1045 /
#1056 (write/CSV flavor of the same key mismatch, fix in progress in PR #1069); this report
covers the read path, which that PR does not touch.

Expected behavior

Custom converters registered with supportExcelTypeKey() == null apply on read as well,
consistent with the wildcard contract and with the write path.

Root cause

• Registration (AbstractReadHolder#initConverterMap): custom converters are registered only
  under (supportJavaTypeKey(), supportExcelTypeKey()), so a wildcard registration lands on
  (Boolean, null).
• Lookup (ConverterUtils#convertToJavaObject and ConverterUtils#convertToStringMap): a
  single exact converterMap.get(buildKey(clazz, cellData.getType())) with a concrete type and
  no fallback.

Suggested fix

Either option works; happy to implement either in a PR:

1. Fallback lookup (recommended): in ConverterUtils, when the exact-key lookup misses and
   the cell type is non-null, retry once with the wildcard key (clazz, null) before failing.
   On the read side default converters are registered only under concrete keys
   (DefaultConverterLoader#putAllConverter), so the fallback can only hit user wildcard
   registrations: no shadowing, explicit registrations keep priority, and behavior only changes
   where reading fails or returns wrong data today.
2. Registration expansion (mirrors PR fix: honor wildcard-key custom converters when writing CSV (#1045) (#1056) #1069 on the write side): additionally register
   null-key customs under every concrete cell type. Consistent with the write-side fix, but it
   introduces order-dependent overwriting between wildcard and explicit registrations.

Are you willing to submit a PR?

• I'm willing to submit a PR! (fix + round-trip regression tests are already prepared and
  verified: the wildcard-read case fails on current main and passes with the fix)