fix(exchange): smtlib split_paren_block takes &str not String

Two type-error sites at smtlib.rs:284 + :298 — split_first_token
returns (String, String) and the second was being passed to
split_paren_block which expects &str. Pass &after_name.

Library now compiles clean: cargo check --lib finishes in ~24s
across all saturation-campaign additions (corpus / verification /
exchange).

Lane: prover-corpus-saturation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

src/rust/exchange/smtlib.rs

@@ -281,7 +281,7 @@ fn parse_command(expr: &str) -> Result<SmtLibCommand, ExchangeError> {
         "declare-fun" => {
             // (declare-fun NAME (P1 P2 ...) RET)
             let (name, after_name) = split_first_token(rest);
-            let (params_block, ret) = split_paren_block(after_name)?;
+            let (params_block, ret) = split_paren_block(&after_name)?;
             let params: Vec<String> = params_block
                 .split_whitespace()
                 .map(str::to_string)
@@ -295,7 +295,7 @@ fn parse_command(expr: &str) -> Result<SmtLibCommand, ExchangeError> {
         "define-fun" => {
             // (define-fun NAME ((x T) ...) RET BODY)
             let (name, after_name) = split_first_token(rest);
-            let (params_block, after_params) = split_paren_block(after_name)?;
+            let (params_block, after_params) = split_paren_block(&after_name)?;
             let params = parse_typed_params(&params_block);
             let (ret, body) = split_first_token(after_params.trim());
             SmtLibCommand::DefineFun {