fix: add cfg(feature = "remote") to ENV_VARS_TO_STORAGE_OPTS constant

The constant was only used in remote feature code but defined unconditionally,
causing dead_code warnings when building without the remote feature.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

rust/lancedb/src/connection.rs

@@ -892,6 +892,7 @@ pub struct ConnectBuilder {
     embedding_registry: Option<Arc<dyn EmbeddingRegistry>>,
 }
 
+#[cfg(feature = "remote")]
 const ENV_VARS_TO_STORAGE_OPTS: [(&str, &str); 1] =
     [("AZURE_STORAGE_ACCOUNT_NAME", "azure_storage_account_name")];