feat: add bytearray: calldata prefix

[broody]

Summary

• Add bytearray: prefix to parse_calldata_value() for Cairo ByteArray multi-felt serialization
• Support string mode (bytearray:hello), quoted string mode (bytearray:"hello world"), and raw bytes mode (bytearray:[0x48,0x65,0x6c,0x6c,0x6f])
• Quoted strings strip surrounding double quotes before encoding, allowing strings with spaces
• Uses cainome_cairo_serde::ByteArray and CairoSerde::cairo_serialize() for correct serialization
• Add 7 tests covering short strings, empty strings, long strings (multi-chunk), raw bytes, empty raw bytes, quoted strings, and quoted empty strings
• Update SKILL.md and LLM_USAGE.md with documentation for the new prefix

Test plan

• cargo build succeeds
• cargo fmt and cargo clippy pass cleanly
• cargo test passes (all 50 tests, including 7 new bytearray tests)
• Short string serialization produces correct felts (0 chunks + pending word)
• Empty string produces [0, 0, 0]
• Long string (>31 bytes) produces correct multi-chunk output
• Raw bytes mode produces identical output to equivalent string mode
• Empty raw bytes [] produces [0, 0, 0]
• Quoted string "hello world" strips quotes and encodes correctly
• Quoted empty string "" produces [0, 0, 0]

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