[FEATURE]: McXtrace Filter.comp (and others) could use the FFAST database directly, instead of going through intermediary datafiles

[ebknudsen]

Based on recent work on Filter.comp #2552 - the following improvement would be plausible.
Include the entire FFAST-database in the distribution (~=2.9MB, so not too bad in terms of size) in sqlite-format.
Coupled with some parsing of chemical formulas it would allow for compounds and elemental layers.

To do this, it'd be required to:

• include and depend on a sqlite library
• build a formula parser
• write an access API that instead of calls to read_table-lib makes SQL-queries, including interpolation in between data-points.
• make sure there are no redistribution issues (licensing etc.) in re-sharing the NIST database

The formula parser could in theory be used together with the normal datafiles, but that may end up being very clunky.

[willend]

For the formula-parser we could potentially leverage the ‘tinyexpr’ code that recently came to McStas share.