style: format the whole tree with cargo fmt (stock defaults, #35)

One-time, mechanical reformat — no functional changes. The tree was not
rustfmt-clean (~1800 hunks across ~100 files); this brings it to stock
`cargo fmt` defaults so a `cargo fmt --check` CI gate can follow.
Behaviour-preserving: 2509 pass / 0 fail / 1 ignored (unchanged baseline),
clippy clean. A .git-blame-ignore-revs entry follows so `git blame`
skips this commit.

src/logging.rs

@@ -60,8 +60,8 @@ pub fn init(path: Option<&Path>) -> Result<PathBuf> {
             .with_context(|| format!("create log directory {}", parent.display()))?;
     }
     let file = open_log_file(&chosen)?;
-    let filter = EnvFilter::try_from_env("RDBMS_PLAYGROUND_LOG")
-        .unwrap_or_else(|_| EnvFilter::new("info"));
+    let filter =
+        EnvFilter::try_from_env("RDBMS_PLAYGROUND_LOG").unwrap_or_else(|_| EnvFilter::new("info"));
     let layer = fmt::layer()
         .with_writer(file)
         .with_ansi(false)
@@ -95,8 +95,7 @@ fn home_dir() -> Option<PathBuf> {
     if let Some(p) = std::env::var_os("HOME") {
         return Some(PathBuf::from(p));
     }
-    if let (Some(drive), Some(path)) =
-        (std::env::var_os("HOMEDRIVE"), std::env::var_os("HOMEPATH"))
+    if let (Some(drive), Some(path)) = (std::env::var_os("HOMEDRIVE"), std::env::var_os("HOMEPATH"))
     {
         let mut combined = PathBuf::from(drive);
         combined.push(path);