docs: add missing backticks in documentation

this improve readability of documentation.
enable associated clippy lint `doc_markdown`

src/block/layout.rs

@@ -21,7 +21,7 @@ pub(crate) struct DataLayout {
 	pub(crate) data_dirs: Vec<DataDir>,
 	markers: HashMap<PathBuf, String>,
 
-	/// Primary storage location (index in data_dirs) for each partition
+	/// Primary storage location (index in `data_dirs`) for each partition
 	/// = the location where the data is supposed to be, blocks are always
 	/// written there (copies in other dirs may be deleted if they exist)
 	pub(crate) part_prim: Vec<Idx>,

src/block/metrics.rs

@@ -6,7 +6,7 @@ use opentelemetry::{global, metrics::*};
 
 use garage_db as db;
 
-/// TableMetrics reference all counter used for metrics
+/// `TableMetrics` reference all counter used for metrics
 pub struct BlockManagerMetrics {
 	pub(crate) _compression_level: ValueObserver<u64>,
 	pub(crate) _rc_size: ValueObserver<u64>,

src/block/rc.rs

@@ -136,14 +136,14 @@ impl BlockRc {
 pub(crate) enum RcEntry {
 	/// Present: the block has `count` references, with `count` > 0.
 	///
-	/// This is stored as u64::to_be_bytes(count)
+	/// This is stored as `u64::to_be_bytes(count)`
 	Present { count: u64 },
 
 	/// Deletable: the block has zero references, and can be deleted
-	/// once time (returned by now_msec) is larger than at_time
+	/// once time (returned by `now_msec`) is larger than `at_time`
 	/// (in millis since Unix epoch)
 	///
-	/// This is stored as [0u8; 8] followed by u64::to_be_bytes(at_time),
+	/// This is stored as [0u8; 8] followed by `u64::to_be_bytes(at_time)`,
 	/// (this allows for the data format to be backwards compatible with
 	/// previous Garage versions that didn't have this intermediate state)
 	Deletable { at_time: u64 },