Show 'Rows Removed by Filter' with two fractional digits in EXPLAIN

Hi,

Since ddb17e387aa, EXPLAIN reports per-loop actual rows with two decimal digits.
The neighbouring counters - Rows Removed by Filter, by Join Filter - are divided
by nloops too, but are still printed with zero digits. In a parameterised inner
side this makes the two numbers contradict each other, for example:

-> Index Scan using tenk1_unique1 on tenk1 b (actual rows=0.90 loops=10)
Index Cond: (unique1 = g.g)
Filter: (ten <> 0)
Rows Removed by Filter: 0

The scan returned 0.90 rows per loop out of 1.00 fetched, yet the filter claims
it removed nothing. See the attached patch for complete examples.

The patch is a single-line change in show_instrumentation_count() plus two
tests. It is a concept, not a finished patch: I have not regenerated the other
expected outputs, where many values will change from "N" to "N.00" - you can
find a sketch for that in 0002-* file. Before going through that churn, I would
like to hear whether people agree that these counters should follow the same
rule as actual rows. The options I see are:

1. Always print two digits, as actual rows do now.
2. Leave the math to users and print exact totals without dividing by nloops.

The second approach is a much bigger change, with obvious pros and cons.
The first one is simpler and more conservative, and it is what the attached
patch does. In [1], depesz describes how the switch to fractional actual rows
affected his explain parser, and it needed only a small fix. So I expect this
change to be similarly harmless for tools.

Thoughts?

[1]
https://www.depesz.com/2025/02/28/waiting-for-postgresql-18-allow-explain-to-indicate-fractional-rows/

--
regards, Andrei Lepikhov,
pgEdge