refactor to use existing sizeCellInner function more

[charliepark]

As I was running #3214 through a few checks and the robot noticed that several locations in the codebase use variations of the code in sizeCellInner to render stylized "size + unit" text on the screen.

The pattern formatBytes(x) → {value} <span className="text-tertiary">{unit}</span> is hand-rolled in several places rather than going through sizeCellInner:

- InstanceResourceCell.tsx:22 — {memory.value} <span className="text-tertiary">{memory.unit}</span>. This is byte-identical to sizeCellInner's output and could just be sizeCellInner(value.memory). The one exact duplicate.
- InstancesPage.tsx:117-120 (memory column) — same shape but the unit span adds ml-1 on top of the literal space, so it's a double gap. Near-duplicate, not identical.
- InstancePage.tsx:222-224 (ram) — split into a text-default span plus a text-tertiary ml-1 span with a leading space.
- SledPage.tsx:78-79 (usable physical ram) — text-default pr-0.5 + text-tertiary.
- SiloQuotasTab.tsx:35 — its own Unit = classed.span\ml-1 text-secondary`(note:text-secondary, not text-tertiary`).

I haven't verified each of these locations, but it seems like we could clean them up pretty easily.

Also note that "sizeCellInner" might make more sense with a different name (and possibly located elsewhere) once these various places in the UI are updated to use the common component / helper.