chore: code improvements

[tinom9]

Description

• Replace raw strip_prefix("0x") / starts_with("0x") calls with canonical hex_utils helpers (strip_0x, require_0x) across trace_renderer.rs and selector_resolver.rs.
• Use parse_rpc_response in fetch_chain_id instead of manual JSON parsing, so HTTP errors (e.g. 502) produce clear status messages instead of misleading "invalid JSON".
• Add is_valid_address / is_valid_tx_hash predicates to hex_utils covering uppercase 0X prefix and hex digit validation; wire them into contract_resolver, validate_address, and a new validate_tx_hash used by tx.rs.
• Replace stringly-typed serde_json::Value indexing with typed Deserialize structs (SelectorEntry, ContractInfo, Compilation) in both sourcify resolvers.
• Inject sourcify base URLs via constructor Option<String> parameter (explicit > env var > default) for test-friendly dependency injection.
• Centralize cache kind strings as constants (SELECTOR_CACHE, CONTRACT_CACHE, ALL_CACHE_KINDS) in disk_cache.rs; remove duplicated CACHE_KINDS from clean.rs.
• Move CallTrace struct from cli/trace.rs to utils/trace_renderer.rs to fix utils/ → cli/ layering violation.
• Emit resolver warnings on Sourcify JSON parse failures, treating them as transient misses.