admission: collapse from two WorkQueues to one

[stevendanna]

Delete resourceTier, cpuTimeTokenChildGranter, and the per-tier
arrays that organized the system into two WorkQueues, two requesters,
and four token buckets. The granter now holds two buckets
(canBurst, noBurst) and implements the granter interface directly.
The coordinator owns a single WorkQueue, and GetKVWorkQueue always
returns it when CTT is enabled (ignoring isSystemTenant).

Settings are consolidated: KVCPUTimeUtilGoal becomes the canonical
target under admission.cpu_time_tokens.target_util.system_tenant is retired.
ConfigSnapshot collapses from per-tier fractions to a single NoBurstFrac.

Epic: none
Release note: None

Co-Authored-By: roachdev-claude roachdev-claude-bot@cockroachlabs.com

[trunk-io]

😎 Merged directly without going through the merge queue, as the queue was empty and the PR was up to date with the target branch - details.

[blathers-crl]

Your pull request contains more than 1000 changes. It is strongly encouraged to split big PRs into smaller chunks.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[stevendanna]

Apologies for the large diff.

[blathers-crl]

Detected infrastructure failure (matched: self-hosted runner lost communication with the server). Automatically rerunning failed jobs. (run link)

[wenyihu6]

nice! glad we are ripping this out in this release. re: commit 2: if the only purpose of the .app_tenant aliases is to keep existing dashboards rendering, is the right move to update the dashboard as part of the upgrade or create a new dashboard instead?

@wenyihu6 made 1 comment.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on joshimhoff and sumeerbhola).

[blathers-crl]

Metrics change detected

This PR adds or updates one or more CRDB metrics. If you want these metrics to be exported by CRDB Cloud clusters to Internal CRL Datadog and/or included in the customer metric export integration (Essential metrics for standard deployment, and Essential metrics for advanced deployment), refer to this Installation and Usage guide of a CLI tool that syncs the metric mappings in managed-service. Run this CLI tool after your CRDB PR is merged.

• The CLI opens a PR in managed-service with the required config changes.
• Please track that PR and ensure it merges so your metrics become available to CRDB Cloud clusters.

Note: Your metric will appear in Internal CRL Datadog only after the managed-service PR merges and the new OTel configuration rolls out to at least one cluster running a CRDB build that includes this metric.

Docs: cockroach-metric-sync

Questions: reach out to @obs-india-prs

[wenyihu6]

Re-running CI - hit an unrelated flake https://mesolite.cluster.engflow.com/invocations/default/eaac9317-1811-4624-a344-8d9a97a1379b (#170845).

[stevendanna]

is the right move to update the dashboard as part of the upgrade or create a new dashboard instead?

I'm OK with this as long as @joshimhoff is

[wenyihu6]

Lets drop the second commit and get the first commit merged first? Don't want this PR to rot. I will stamp if you open a new PR with the second commit, and we can dabate more on it.

[stevendanna]

/trunk merge