Add support for scalar-unit data type

See packaging spec for details and supported units.

**scalar-unit types**
Scalar-unit types can be used to define scalar values along with a unit from the list of recognized units (a subset of GNU units) provided below.

Grammar:
```
inputs:
:
```

Unit Description
B, byte
kB, kilobyte (1000 bytes)
MB, megabyte (1000000 bytes)
GB, gigabyte (1000000000 bytes)
TB, terabyte (1000000000000 bytes)

TBD: we could allow for any case combination and say we normalize to the unit case?

d, days
h, hours
m, minutes
s, seconds
ms, milliseconds
us, microseconds

Start with the packaging spec and locate the entry point that parses and validates package input types. Define scalar-unit values using the listed byte and time units, resolve the open question about case normalization, and verify that valid units are accepted and unsupported units are rejected.

Written by the indexing model from the issue text.