Speed up formatting

[Geod24]

Just running a basic reporting on the first 19 Mbs of blocks:

   8.79%  libbtc   libbtc              [.] _D3std6format__T14formatUnsignedTSQBgQBf__T7sformatTaTxhZQoFAaxAaxhZ4SinkTmTaZQCkFNaNfKQCcmKxSQDoQDn__T10FormatSpecTaZQpkbZv
   5.76%  libbtc   libbtc              [.] _D3std6format__T10FormatSpecTaZQp6fillUpMFNaNfZv
   4.48%  libbtc   libbtc              [.] _D3std6digest3sha__T3SHAVki512Vki256ZQr__T12T_SHA2_16_79TkZQrFNaNbNiNfiKG16kkkkKkkkkKkkZv
   4.38%  libbtc   libbtc              [.] _D3std6format__T7sformatTaTxhZQoFAaxAaxhZ4Sink3putMFNaNbNfAxaZv
   3.60%  libbtc   libbtc              [.] _D3std6format__T14formattedWriteTSQBgQBf__T7sformatTaTxhZQoFAaxAaxhZ4SinkTaTxhZQClFNaNfQCcxQBcxhZk
   2.56%  libbtc   libbtc              [.] _d_arraycopy
   2.46%  libbtc   libbtc              [.] _D3std6format__T10FormatSpecTaZQp__T17writeUpToNextSpecTSQCdQCc__T7sformatTaTxhZQoFAaxAaxhZ4SinkZQCjMFNaNfKQBzZb
   2.20%  libbtc   libbtc              [.] _D3std6digest3sha11rotateRightFNaNbNiNfkkZk