A <python> variable block previously saw only the parameters of the single
collection the variable is linked to via 'col', injected as bare names plus
par[]/parErr[]. To compute variables for several collections one therefore
needed a separate block per collection.
Now every loaded collection is additionally injected as coll[]/collErr[]
dictionaries, addressable both by integer index (matching 'col <idx>' /
'select <idx>') and by collection name; index and name keys reference the same
per-parameter dict. A single block placed after all 'var = python' declarations
can thus compute - and combine - variables for any collection, e.g.
coll[0]['Sigma'] or coll['NAME.db']['Sigma'].
The bound-collection bare names / par[] / parErr[] are unchanged, so existing
scripts and GUI variables keep working. The collection list is threaded through
PmuppScript::var_cmd and the GUI add()/check() paths into PVarHandler.
Verified: a one-block script using both an index key and a name key reproduces
the numeric output of the equivalent two-block script bit-for-bit.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>