Give probe_result duration sub-second precision

[lewispb]

Problem

After the SQLite → MySQL migration, the duration of most probe results renders as 0.00s in production.

The duration column is declared as t.decimal :duration with no precision (db/migrate/20250114000001_create_upright_probe_results.rb). Duration is computed from a monotonic clock and is almost always sub-second:

# app/models/concerns/upright/probeable.rb
def measure
  start_time = monotonic_now
  result = yield
  [ result, monotonic_now - start_time ]   # float seconds, e.g. 0.043
end

On SQLite, NUMERIC affinity stored the full float (0.043). On MySQL, DECIMAL with no scale defaults to DECIMAL(10,0) — zero digits after the point — so every value is rounded to a whole second on write:

• 0.043s → 0
• 0.6s → 1

Most checks finish well under a second, so they store 0 and display as 0.00s.

Fix

New migration altering the column to DECIMAL(10,6) (microsecond precision; max ~9999s). Dummy schema dump updated to match.

Caveats

• Rows already written as 0 were rounded on insert and cannot be recovered; only probe results recorded after the migration runs will be correct.
• This is the engine migration that runs in host apps (e.g. 37upright) via the appended migration path, so deploying the bumped gem fixes production. Host bump: basecamp/37upright (companion PR).

🤖 Generated with Claude Code

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