Add data and aria attribute expansion helpers

[sbsoftware-agent]

Summary

• add data: / aria: container handling in AttributeHash so entries expand to data-* / aria-*
• support value serialization for String, Bool, and numeric values; omit attributes for Nil
• normalize container keys for symbol/string input by converting underscores to hyphens and avoiding double prefixes
• define merge precedence so explicit data-* / aria-* attributes override data: / aria: entries
• apply the same behavior across named args, tuple sources, array composition, and to_html_attrs
• extend void-tag attribute composition to accept tuple sources consistently with normal tags
• document usage and precedence with a README example

Tests

• added spec/instance_template/data_aria_attributes_spec.cr covering:
  • basic expansion
  • type serialization and nil omission
  • merge behavior across array/tuple/to_html_attrs/named args
  • key normalization rules
• ran:
  • CRYSTAL_CACHE_DIR=/tmp/.crystal-cache-html crystal spec
  • CRYSTAL_CACHE_DIR=/tmp/.crystal-cache-html crystal spec spec/instance_template/data_aria_attributes_spec.cr

[sbsoftware]

I think the whole "precedence of explicit attributes" feature bloats the code while bringing little value. Let's just implement it the least surprising way - who comes last, wins.

[sbsoftware-agent]

Implemented as requested: precedence tracking was removed and merge behavior is now simple last-write-wins based on encounter order.

What changed:

• removed explicit-priority bookkeeping and related branching from AttributeHash
• duplicate data-* / aria-* assignments now overwrite by order, regardless of source (tuple, array, to_html_attrs, named args, data:/aria: maps)
• updated specs to assert last-write-wins semantics
• updated README wording/example to document last-write-wins behavior

[sbsoftware]

Please audit the code for possible simplifications and redundancies to remove I've given one hint in a line comment, but there's probably more to discover. Try to inline code rather than using helper methods.

[sbsoftware-agent]

Done. I audited src/attribute_hash.cr for simplifications and removed redundant helpers, favoring direct inline flow where practical.

Simplifications made:

• inlined data/aria prefix detection in []= (removed prefixed_hash_prefix)
• inlined hash-entry normalization/validation inside assign_prefixed_hash loops
• removed assign_prefixed_hash_entry
• removed normalize_prefixed_hash_key and normalize_prefixed_hash_key_part
• removed serialize_prefixed_value and replaced with direct assign_prefixed_value overloads (Nil delete vs generic to_s assign)

Validation:

• CRYSTAL_CACHE_DIR=/tmp/.crystal-cache-html crystal spec (37 examples, 0 failures)

Committed as 181b2f4.