Fix format ~f and update tests (3rd)

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I found following error cases.
```
(a) (format "~1,0F" 1.5)       -> "1."
(b) (format "~1,0F" (/. 1 0))  -> "+inf."
(c) (format "~1,0F" (/. -1 0)) -> "-inf."
(d) (format "~1,0F" (/. 0 0))  -> "+nan."
```

For (a), (format "~1,0F" 1.5) must return "2."
because 'round' of Scheme uses banker's rounding.

The reason of (a) is that integer part and fractional part
were processed separately.

For (b)-(d), it is necessary to check +inf.0, -inf.0, +nan.0, -nan.0.

I fixed these cases and updated tests.

I created a pull request as follows.
https://github.com/scheme-requests-for-implementation/srfi-48/pull/4

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<div dir=3D"ltr"><div>I found following error cases.</div><div>```</div><di=
v>(a) (format &quot;~1,0F&quot; 1.5)=C2=A0 =C2=A0 =C2=A0 =C2=A0-&gt; &quot;=
1.&quot;</div><div>(b) (format &quot;~1,0F&quot; (/. 1 0))=C2=A0 -&gt; &quo=
t;+inf.&quot;</div><div>(c) (format &quot;~1,0F&quot; (/. -1 0)) -&gt; &quo=
t;-inf.&quot;</div><div>(d) (format &quot;~1,0F&quot; (/. 0 0))=C2=A0 -&gt;=
 &quot;+nan.&quot;</div><div>```</div><div><br></div><div>For (a), (format =
&quot;~1,0F&quot; 1.5) must return &quot;2.&quot;</div><div>because &#39;ro=
und&#39; of Scheme uses banker&#39;s rounding.</div><div><br></div><div>The=
 reason of (a) is that integer part and fractional part=C2=A0</div><div>wer=
e processed separately.</div><div><br></div><div>For (b)-(d), it is necessa=
ry to check +inf.0, -inf.0, +nan.0, -nan.0.</div><div><br></div><div>I fixe=
d these cases and updated tests.</div><div><br></div><div><div>I created a =
pull request as follows.</div><div><a href=3D"https://github.com/scheme-req=
uests-for-implementation/srfi-48/pull/4">https://github.com/scheme-requests=
-for-implementation/srfi-48/pull/4</a></div></div><div><br></div></div>

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