Cut steady-state log noise from miren server

[phinze]

After a v0.7.0 upgrade on one of our prod servers we pulled two hours of journalctl -u miren and ran a frequency analysis. The server was producing around 86k lines in that window — roughly 75% DEBUG and 24% INFO — and most of it was content-free steady-state chatter. Every internal RPC logged its own auth success, every proxied HTTP request logged its route match, every sandbox-pool reconcile emitted a three-line trio, every lease got a heartbeat line, every sandbox no-op got a two-line "I checked, nothing to do" pair. Finding anything interesting in the log stream was genuinely hard.

This PR is the straightforward cut: remove the lines that are pure noise and delete the Processing event INFO line in the generic controller framework, which was the single loudest prod-visible offender because it fires for every reconcile of every entity. Also took out a redundant container stats log — that data already flows into the customer metrics pipeline under metrics/, so the slog copy was just duplication.

The ticket suggested some of these could be downgraded to TRACE instead, but the codebase uses stdlib slog with only Debug/Info/Warn/Error. Rather than introduce a custom TRACE level just for this, we deleted outright — git log -S will find anything we want back.

A few offenders were actually metrics wearing a trenchcoat. The OTel SDK is already set up in pkg/rpc/otel.go, but we don't currently emit any first-party Counter / Histogram / UpDownCounter instruments from the server itself. Ingress request counts, controller reconcile counts, and sandbox pool gauges all belong there rather than in the log stream. That's its own project, tracked as MIR-1026. The failed to lock file chatter from embedded etcd's purge routine (240× in 2h) is library-internal and needs its own intervention, tracked as MIR-1025.

Extrapolating from the ticket's volume numbers, this removes roughly 65k of the 86k lines per 2h (~76%).

Closes MIR-1024
Related: MIR-1025, MIR-1026

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• controllers/sandbox/sandbox_frozen_test.go

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📝 Walkthrough

Walkthrough

This pull request removes debug/info log statements across eight source files (deployment launcher, sandbox metrics/controller/sandbox, sandbox pool manager, controller reconciliation, RPC server, and HTTP ingress). No control flow, error handling, or functional behavior was changed. Additionally, the frozen SHA-256 expected hash for sandbox.go in a frozen test was updated; no other test logic was modified.

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