settings: surface validation bounds for numeric cluster settings

[lohitkolluri]

Summary

Cluster settings now expose their validation bounds. The valid range for settings like kv.snapshot_rebalance.max_rate was hidden inside the validator, so users had to discover it by trial and error or by reading error messages. This change records the min and max on each setting and shows them in the generated settings list.

Informs #172035.

What changed

Two commits.

1. Record bounds on each setting. The four numeric setting types (int, byte size, float, duration) now store their min and max values, exposed via a new Bounds() method.

2. Show bounds in the settings list. cockroach gen settings-list (and the generated docs it produces) now includes Min and Max columns showing the valid range for each numeric setting.

Out of scope

• The upper-exclusive range option only reports the inclusive range today.
• Surfacing bounds in SHOW CLUSTER SETTING, the internal settings table, and the admin HTTP API. The data is now available; making it visible there is a follow-up.

Testing

• Added a test file covering every numeric validation option.
• The settings package tests pass.
• Formatter is clean.
• Spot-checked the generated docs against representative settings (e.g. sql.trace.txn.sample_rate shows Min=0, Max=1; kv.snapshot_rebalance.max_rate shows Min=1048576, no max).

AI disclosure: Drafted with assistance from Claude Code.

Epic: CRDB-37791

[blathers-crl]

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

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I have added a few people who may be able to assist in reviewing:

• @rytaft (author of settings: validation bounds (Min/Max) are not surfaced in docs or SHOW CLUSTER SETTING #172035)

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[blathers-crl]

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

Thank you for updating your pull request.

Before a member of our team reviews your PR, I have some potential action items for you:

• We notice you have more than one commit in your PR. We try break logical changes into separate commits, but commits such as "fix typo" or "address review commits" should be squashed into one commit and pushed with --force
• When CI has completed, please ensure no errors have appeared.

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[lohitkolluri]

Heads-up: this PR covers items 1 and 2 from the issue's expected behavior:

• Adding the Bounds() accessor for numeric settings.
• Surfacing those bounds in the docs generator.

Item 3 (SHOW ALL CLUSTER SETTING(S), crdb_internal.cluster_settings, and /_admin/v1/settings) is intentionally out of scope for this PR. The necessary plumbing is already in place, so wiring those up should be a straightforward follow-up.

I'm happy to open a separate PR for that if you'd prefer, or leave it for whoever picks it up next.

[rytaft]

Thanks for the contribution @lohitkolluri! I've requested a review from the owning team for cluster settings infra.

Item 3 (SHOW ALL CLUSTER SETTING(S), crdb_internal.cluster_settings, and /_admin/v1/settings) is intentionally out of scope for this PR. The necessary plumbing is already in place, so wiring those up should be a straightforward follow-up.

I'm happy to open a separate PR for that if you'd prefer, or leave it for whoever picks it up next.

Separate PR sounds good, but in that case please change "Fixes #172035" to say "Informs" so the issue doesn't get auto-closed.

[lohitkolluri]

Thanks! I've updated the PR to use "Informs #172035" instead of "Fixes #172035". I'll handle item 3 in a separate follow-up PR.