fix(source): resolve avro Ref during access without hack

[xiangjinwu]

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What's changed and what's your intention?

Sequel to #19601 and resolves #17020.

The recursive call is changed from Self {schema: inner, relax_numeric: self.relax_numeric}.convert_to_datum(v, field_type) into self.convert_to_datum(inner, v, field_type) so that

• The changing part schema: inner is passed as argument rather than keep reconstructing new AvroParseOptions.
• self: AvroParseOptionsInner captures the immutable "global" context: relax_numeric: bool and refs: NamesRef<'a>

On the use site, self.schema is changed to self.lookup_ref(unresolved_schema). Note that introducing a new type to distinguish resolved from unresolved would not make it less error-prone for a careless developer - nothing prevents them from matching against unresolved apache_avro::Schema directly and ignoring Schema::Ref.

Full removal of ResolvedAvroSchema will be done in an immediate follow-up, to minimize the signature changes in this PR. ResolvedAvroSchema will either be fully removed or repurposed to hold HashMap<Name, Schema> (an owned NamesRef) in a follow-up.

Same as #19601, this is intended to be part of v2.2 and NOT cherry-picked into earlier versions.

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[xxchan]

:GTM

[xiangjinwu]

Now we can support reference to a decimal or a record containing a decimal field.