Add DynamicOpenDataflowGraph acceleration data structures

[elliottslaughter]

Definitely not in a final state yet, but sending this draft PR to show what I'm doing to accelerate the DynamicOpenDataflowGraph value lookup data structures.

TODO:

• Refactor DynamicOpenDataflowGraph as a proper class and encapsulate its implementation

Notes to self:

• Ordered set/map are ferociously slow due to large keys (DynamicNodeInvocation/DynamicValueAttrs). This is, strictly speaking, a constant factor, but it's massive: > 10x in some cases. The larger and more important issues are reducing the number of calls to operator< via better algorithms, but it's worth keeping in mind that e.g., a naive bidict<dynamic_node_invocation_id_t, DynamicNodeInvocation> is by itself a 6x slowdown if you aren't careful.
• Almost everything else here is of the flavor "O(N^2) is catastrophic, switch to an O(N) algorithm". The constant factors are particularly bad because of the above but almost anything will dominate in an O(N^2) algorithm when N is sufficiently large.

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