Rework tracing, bump deps, turn disk cache on

[ferd]

When dealing with various installs, I found out that my context propagation was messy. This is unsurprising because I was just sending literal internal context values from OTel without converting them nor exporting them, so when two ReVault instances had different OTel internals, context got lost.

This replaces things by making the context propagation explicit with the adequate serialization functions.

All of these are wrapped into new shared calls (in revault_otel, but could move to another internal app at some point) that essentially make things work the way with_span(...) works in the OTel lib, excepts split up between ?start_active_span/1-2 and ?end_active_span/0 and uses the pdict to maintain the context stack required. Additionally, the functions to extract the trace state to send it across services is used everywhere, even inside services to keep things portable and modifiable.

While at it, I've added TLS-specific traces for the client and server, and moved these to their own hierarchy outside of the connection span and into the higher session-level stuff such that the traces are more readable.

Also:

• other deps are bumped
• disk cache is on by default in non-test situations given how much faster it is and lots of personal testing made it feel safer.