Fix Runtime::snapshot access to GraphEntry node

[YuMuuu]

Summary

Fix Runtime::snapshot() to access getProperties() through the
GraphNode stored in each GraphEntry.

nodeTable maps NodeId to GraphEntry, but GraphEntry itself does not
provide getProperties(). The method belongs to GraphEntry::node.

This regression appears to have been introduced in
a8923b8, when the mapped type of
nodeTable was changed from std::shared_ptr<GraphNode<FloatType>> to
GraphEntry.

Reproduction

At commit 60e7234, run the following from the repository root:

❯ printf '#include "elem/Runtime.h"\nvoid test(elem::Runtime<float>& r)
{ (void)r.snapshot(); }\n' \
| c++ -Iruntime -std=c++17 -fsyntax-only -x c++ -
In file included from <stdin>:1:
runtime/elem/Runtime.h:495:50: error: member reference type 'std::tuple_element<1, std::pair<const int, elem::Runtime<float>::GraphEntry>>::type' (aka 'elem::Runtime<float>::GraphEntry') is not a pointer; did you mean to use '.'?
          ret.insert({nodeIdToHex(nodeId), node->getProperties()});
                                           ~~~~^~
                                               .
<stdin>:3:11: note: in instantiation of member function 'elem::Runtime<float>::snapshot' requested here
{ (void)r.snapshot(); }
        ^
In file included from <stdin>:1:
runtime/elem/Runtime.h:495:52: error: no member named 'getProperties' in 'elem::Runtime<float>::GraphEntry'
          ret.insert({nodeIdToHex(nodeId), node->getProperties()});
                                           ~~~~  ^
2 errors generated.

Compilation fails with:

error: no member named 'getProperties' in 'elem::Runtime::GraphEntry'

The regular native build does not detect this because Runtime is a class
template and snapshot() is not instantiated unless it is used.

Change:

node->getProperties()

to:

entry.node->getProperties()

The reproduction command succeeds after this change.

[YuMuuu]

This likely affects all releases from v4.0.0 through v4.0.8.

a8923b8#diff-09113ad3ada3d29ef5720cd1d63e85b7a05ef4e3885f217f861f00d7d15f719e