extract module path info from DWARF

[japaric]

while doing #19 it seemed possible to also compute the module path (krate::module::function) of each log statement.
we could include that info in the probe-run output as a lighter version alternative to the full path (or as complementary info)

implementation notes:

• while traversing the DIE (Debugging Information Entry) tree
• when entering a DW_TAG_namespace node read the DW_AT_name attribute and use that as a segment; push that into a path
• when leaving the DW_TAG_namespace node remove (pop) the segment you added to path
• when you encounter a DEFMT_LOG_STATEMENT variable (a log statement) attach the current path to it
• I recommend running dwarfdump on the firmware image you are working on to visualize the DIE tree
• I'm unsure if DIE from other crates need special handling