Fix decoding fixed length arrays of struct in python sbp2json [AP-946] (

#1378)

# Description

@swift-nav/devinfra

Alter the python decoding generated code so that fixed length arrays
which contain structs (as opposed to primitive types) are properly
decoded with the correct parser for the filled type.

Variable length arrays are already decoded properly in all cases, it's
only fixed length arrays which are broken. Only the python binding are
affected by this bug.

# API compatibility

Sort of.

The output of the python version of `sbp2json` changes.

Currently messages which contain a fixed length array of structs are
decoded as byte arrays in the python version of sbp2json. This is
misleading.

The rust version of sbp2json is able to decode these constructs
properly. Therefore the output of the python and rust version of
`sbp2json` can differ given identical inputs.

In the current definition there are only 3 message types which suffer
from this behaviour - `MsgTrackingIq`, `MsgTrackingIqDepA`,
`MsgTrackingIqDepB` - all very rare and not really seen in the wild.

Therefore compatibility risk is practically zero.

## API compatibility plan

None required

# JIRA Reference

https://swift-nav.atlassian.net/browse/AP-946

generator/sbpg/targets/python.py

@@ -72,7 +72,7 @@ def construct_format(f, type_map=CONSTRUCT_CODE):
     f_ = copy.copy(f)
     f_.type_id = fill
     s = f.options.get('size', None).value
-    return "'{id}' / construct.Array({size}, {type})".format(id=f.identifier, size=s, type=type_map.get(f_.type_id, 'construct.Byte'))
+    return "'{id}' / construct.Array({size}, {type})".format(id=f.identifier, size=s, type=type_map.get(f_.type_id, f'{fill}._parser'))
   elif f.type_id == 'array':
     fill = f.options['fill'].value
     if type_map.get(fill):

python/sbp/RELEASE-VERSION

@@ -1 +1 @@
-5.0.3
+5.0.3

python/sbp/tracking.py

@@ -887,7 +887,7 @@ class MsgTrackingIq(SBP):
   _parser = construct.Struct(
                    'channel' / construct.Int8ul,
                    'sid' / GnssSignal._parser,
-                   'corrs' / construct.Array(3, construct.Byte),)
+                   'corrs' / construct.Array(3, TrackingChannelCorrelation._parser),)
   __slots__ = [
                'channel',
                'sid',
@@ -992,7 +992,7 @@ class MsgTrackingIqDepB(SBP):
   _parser = construct.Struct(
                    'channel' / construct.Int8ul,
                    'sid' / GnssSignal._parser,
-                   'corrs' / construct.Array(3, construct.Byte),)
+                   'corrs' / construct.Array(3, TrackingChannelCorrelationDep._parser),)
   __slots__ = [
                'channel',
                'sid',
@@ -1097,7 +1097,7 @@ class MsgTrackingIqDepA(SBP):
   _parser = construct.Struct(
                    'channel' / construct.Int8ul,
                    'sid' / GnssSignalDep._parser,
-                   'corrs' / construct.Array(3, construct.Byte),)
+                   'corrs' / construct.Array(3, TrackingChannelCorrelationDep._parser),)
   __slots__ = [
                'channel',
                'sid',