Merge #116: Create wallet dir only when necessary

bff2d37 `open_database` avoids creating a wallet dir if... ...not necessary (Daniela Brozzoni)

Pull request description:

  ### Description

  Making sure to create the wallet dir only when necessary (database is either sqlite or key-value)

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk-cli/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

  #### New Features:

  * [ ] I've added tests for the new feature
  * [ ] I've added docs for the new feature
  * [ ] I've updated `CHANGELOG.md`

  #### Bugfixes:

  * [ ] This pull request breaks the existing API
  * [ ] I've added tests to reproduce the issue which are now passing
  * [ ] I'm linking the issue being fixed by this PR

ACKs for top commit:
  rajarshimaitra:
    tACK bff2d37

Tree-SHA512: ee019830269f5d8332043ef8de750930883eed1791c867da048bd72c945dc576f74e5178b6c0a27737b0035208f7c862cf44c90321dd2bf6f74900fab08e113b

src/utils.rs

@@ -164,6 +164,11 @@ pub(crate) fn prepare_home_dir(home_path: Option<PathBuf>) -> Result<PathBuf, Er
 }
 
 /// Prepare bdk_cli wallet directory.
+#[cfg(any(
+    feature = "key-value-db",
+    feature = "sqlite-db",
+    feature = "compact_filters"
+))]
 fn prepare_wallet_dir(wallet_name: &str, home_path: &Path) -> Result<PathBuf, Error> {
     let mut dir = home_path.to_owned();
 
@@ -178,6 +183,7 @@ fn prepare_wallet_dir(wallet_name: &str, home_path: &Path) -> Result<PathBuf, Er
 }
 
 /// Prepare wallet database directory.
+#[cfg(any(feature = "key-value-db", feature = "sqlite-db",))]
 fn prepare_wallet_db_dir(wallet_name: &str, home_path: &Path) -> Result<PathBuf, Error> {
     let mut db_dir = prepare_wallet_dir(wallet_name, home_path)?;
 
@@ -248,12 +254,14 @@ pub(crate) fn prepare_electrum_datadir(home_path: &Path) -> Result<PathBuf, Erro
     Ok(dir)
 }
 
+#[allow(unused_variables)]
 /// Open the wallet database.
 pub(crate) fn open_database(
     wallet_opts: &WalletOpts,
     home_path: &Path,
 ) -> Result<AnyDatabase, Error> {
     let wallet_name = wallet_opts.wallet.as_ref().expect("wallet name");
+    #[cfg(any(feature = "key-value-db", feature = "sqlite-db",))]
     let database_path = prepare_wallet_db_dir(wallet_name, home_path)?;
 
     #[cfg(feature = "key-value-db")]