feat(file_reader): swap std::deque for small_fifo

Significantly improves `file_reader` performance, especially when used
with `libc++`, where `std::deque` causes a significant regression due
to its larger block size.

```
Summary
  libc++/dwarfsck.fifo8 -i perl-install-small-v0.7.5.dwarfs --checksum sha256 ran
    1.00 ± 0.03 times faster than libstdc++/dwarfsck.fifo16 -i perl-install-small-v0.7.5.dwarfs --checksum sha256
    1.00 ± 0.03 times faster than libc++/dwarfsck.fifo4 -i perl-install-small-v0.7.5.dwarfs --checksum sha256
    1.01 ± 0.04 times faster than libstdc++/dwarfsck.deque -i perl-install-small-v0.7.5.dwarfs --checksum sha256
    1.02 ± 0.03 times faster than libc++/dwarfsck.fifo16 -i perl-install-small-v0.7.5.dwarfs --checksum sha256
    1.03 ± 0.04 times faster than libc++/dwarfsck.fifo32 -i perl-install-small-v0.7.5.dwarfs --checksum sha256
    1.31 ± 0.04 times faster than libc++/dwarfsck.deque -i perl-install-small-v0.7.5.dwarfs --checksum sha256
```

Author: mhx

src/reader/detail/file_reader.cpp

@@ -28,10 +28,10 @@
 
 #include <array>
 #include <cassert>
-#include <deque>
 #include <numeric>
 
 #include <dwarfs/binary_literals.h>
+#include <dwarfs/container/small_fifo.h>
 #include <dwarfs/detail/file_view_impl.h>
 #include <dwarfs/reader/detail/file_reader.h>
 #include <dwarfs/reader/filesystem_v2.h>
@@ -110,10 +110,13 @@ class block_range_iterable::state {
   }
 
  private:
+  template <typename T>
+  using fifo_t = container::small_fifo<T, 8>;
+
   filesystem_v2_lite const& fs_;
   uint32_t inode_;
-  std::deque<file_range> ranges_;
-  std::deque<std::future<block_range>> pending_;
+  fifo_t<file_range> ranges_;
+  fifo_t<std::future<block_range>> pending_;
   file_size_t current_bytes_{0};
   file_size_t pending_bytes_{0};
   file_size_t remaining_{0};