[feature] Refactor Concurrency

[KCarretto]

What type of PR is this?

/kind feature

What this PR does / why we need it:

• Introduces eldritch::runtime::Message and associated message types for communication between the caller and an eldritch runtime (on separate threads)
• Fixes a bug where imix would leave open an established connection (forever)
• Fixes some Tavern issues
• Adds a small rate limit to imix, to prevent overloading SQLlite (1req/25ms)
• Implements a file.report API for sending files to tavern

Which issue(s) this PR fixes:

No one asked for this

[hulto]

Couple thoughts

[hulto]

It's unclear what's happening here - but I think we want imix install to print in realtime similar to golem.

[KCarretto]

This does not change any behavior, but currently this will print all output after evaluation. The print_stdout is a feature flag we likely don't want enabled for imix.

[codecov]

Codecov Report

Attention: 271 lines in your changes are missing coverage. Please review.

Comparison is base (acaae92) 67.09% compared to head (9de85fe) 70.49%.

Files	Patch %	Lines
...s/lib/eldritch/src/runtime/messages/report_file.rs	0.00%	55 Missing ⚠️
implants/lib/transport/src/mock.rs	0.00%	35 Missing ⚠️
implants/lib/transport/src/grpc.rs	0.00%	20 Missing ⚠️
implants/imix/src/task.rs	0.00%	19 Missing ⚠️
implants/imix/src/install.rs	0.00%	16 Missing ⚠️
.../lib/eldritch/src/runtime/messages/report_error.rs	0.00%	16 Missing ⚠️
...lib/eldritch/src/runtime/messages/report_finish.rs	0.00%	16 Missing ⚠️
.../lib/eldritch/src/runtime/messages/report_start.rs	0.00%	16 Missing ⚠️
...s/lib/eldritch/src/runtime/messages/report_text.rs	15.78%	16 Missing ⚠️
implants/lib/eldritch/src/runtime/messages/mod.rs	7.14%	13 Missing ⚠️
... and 8 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #599      +/-   ##
==========================================
+ Coverage   67.09%   70.49%   +3.40%     
==========================================
  Files         147      159      +12     
  Lines        9741    10488     +747     
==========================================
+ Hits         6536     7394     +858     
+ Misses       3026     2915     -111     
  Partials      179      179              

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[Cictrone]