make traces own proxies and bsyms

[t-vi]

Currently, we do not guard against inconsistencies in traces resulting from proxies not being linked to them except through the names attribute.

This proposes to change it:

• make the "names" set into a dict name->proxy,
• make Proxy.owning_trace / BoundSymbol.owning_trace a weak ref to the owning trace,
• have a mechanism to copy proxies and bsyms to a trace,
• enforce (at least in debug mode but maybe in general?) that a proxy/bsym is used in a trace only if it is in names and the owning trace is using it.

Note that many of the hard to debug "key error" issues in 2024 came from inconsistencies that would be disallowed.

cc @apaz-cli

[mruberry]

Do we need to update our tooling for trace transformations before/when we do this?

[t-vi]

Yes. It is a rather large change, but it will be a huge QOL improvement avoiding things that lead to subtle bugs today.
Note that we have consistency issues (eg. mixing "old trace symbols" and "new trace symbols" in the visitor transformation leading to inconsistent shape data) with the tooling at the moment, so the required tooling changes are probably in places we need to work on.