precomp decorator support

Precomp functions are specified with the @nb.precomp decorator to BudgetItem.calc() methods. The are supplied with the freq array and the ifo struct, their output are supplied as keyword arguments to the wrapped calc(), and their output is cached to prevent re-calculating the same functions multiple time per budget run.

gwinc/io.py

@@ -71,7 +71,7 @@ def _load_hdf5_v1(f):
         )
     trace = read_recursive(f['/traces'])
     trace.name = 'Total'
-    trace.freq = f['Freq'][:]
+    trace._freq = f['Freq'][:]
     attrs = dict(f.attrs)
     if 'ifo' in attrs:
         try:
@@ -105,7 +105,7 @@ def _load_hdf5_v2(f):
         else:
             trace = read_recursive(item)
             trace.name = name
-    trace.freq = freq
+    trace._freq = freq
     trace.ifo = None
     attrs = dict(f.attrs)
     ifo = attrs.get('ifo')