What?

Fixes a compilation hang that occurred when the print_cache_item_size debug feature was enabled,
and cleans up the surrounding instrumentation code.

Root cause of the hang (double lock / deadlock):

During persist_snapshot, the storage iterates over all modified tasks. For each task it calls:

let inner = self.shard.storage.map.get(&task_id).unwrap();
//          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
//          acquires a READ lock on the DashMap shard for task_id
let item = (self.shard.process)(task_id, &inner, &mut self.buffer);

The process closure receives &TaskStorage while that read lock is still held. Inside the
closure, the old code called:

self.get_task_name(task_id, turbo_tasks)

get_task_name creates an ExecuteContext, then calls ctx.task(task_id, TaskDataCategory::Data),
which calls storage.access_mut(task_id), which calls self.map.entry(key). That entry() call
tries to acquire a write lock on the same DashMap shard — which is already read-locked on the
same thread. parking_lot::RwLock is not reentrant, so the thread blocks forever waiting for its
own read lock to be released.

Fix: the &TaskStorage reference (inner) is already in scope inside the closure. Call
inner.get_persistent_task_type() directly instead of going through get_task_name, which avoids
any additional lock acquisition.

Additional changes in this PR:

1. Make compressed-size reporting opt-in — split print_cache_item_size into two Cargo features.
   The base feature now shows uncompressed sizes only (no lz4 overhead). A new
   print_cache_item_size_with_compressed feature re-enables compressed-size reporting for when
   you need it.

2. Extract helpers to eliminate duplication — the output block repeated #[cfg]-gated
   FormatSizes { … } struct literals six times and duplicated the task_name computation twice.
   Extract:

   • FormatSizes struct + impl Display (with #[cfg] isolated inside)
   • TaskCacheStats::task_name(storage) — single source for the grouping key
   • TaskCacheStats::sort_key() — encapsulates the #[cfg]-switched primary sort field
   • TaskCacheStats::format_total/data/avg_data/meta/avg_meta() — each returning FormatSizes

Why?

The compilation was hanging and unusable. The lock ordering bug was non-obvious because the re-entrant
acquisition happened across an abstraction boundary (get_task_name hiding the access_mut call).

How?

Avoid the redundant lock by using the &TaskStorage already provided to the closure.
Pure refactor for everything else — no behaviour change for any given feature combination.