solana: final schema touchups

[sistemd]

• replace status flag with optional error string
• add tx version field
• remove deprecated ui_amount field from the scheme

[claude]

Code Review Summary

This PR makes schema changes to the Solana transaction table:

1. Replaces status: bool with err: Option<String> for richer error information
2. Adds tx_version field to track legacy vs v0 transactions
3. Removes deprecated ui_amount field from token balances

Critical Issue

Schema mismatch in ui_token_amount_builder(): The builder function still includes the ui_amount: Float64 field (lines 638-653) but the schema definition ui_token_amount_dtype() no longer has it. This will cause runtime errors when building Arrow arrays.

Other Items

• Unused Float64Builder import after removing ui_amount
• Minor code simplification opportunities (identity maps)
• Question about the pattern matching consuming message in extractor.rs (may need &message borrow)

The overall approach of serializing errors as JSON strings is pragmatic - it keeps the schema stable while preserving error details for debugging.