error when depending on a library that includes latest version of `kotlinx.datetime`

Sample Notebook that exposes the bug is at the bottom of this description.

If I use `lets-plot` in a Kotlin Notebook and the notebook depends on a library that pulls in the latest `kotlinx.datetime`, I get

```
java.lang.NoSuchMethodError: 'kotlinx.datetime.LocalDateTime kotlinx.datetime.TimeZoneKt.toLocalDateTime(kotlinx.datetime.Instant, kotlinx.datetime.TimeZone)'
at org.jetbrains.letsPlot.commons.intern.datetime.Instant.toDateTime(Instant.kt:28)
at org.jetbrains.letsPlot.commons.formatting.datetime.DateTimeFormatUtil.format(DateTimeFormatUtil.kt:37)
```

even if I'm using `java.time.Instant` in my data. (See notebook details at the bottom.)

This Kotlin Notebook works fine if it does depend on the library with the latest `kotlinx.datetime`.

`lets-plot` currently uses `kotlinx.datetime` at 0.6.2.

There are incompatibilities between this and the latest version of `kotlinx.datetime` (currently 0.7.1).

This ticket is to upgrade `lets-plot` to the latest version of `kotlinx.datetime`.

Sample Notebook:

```
%use dataframe
%use lets-plot
---
import java.math.BigDecimal

val simple = dataFrameOf("a", "b")(java.time.Instant.parse("2026-04-05T00:00:00Z"), BigDecimal.valueOf(2.0))
simple.schema()
---
a: java.time.Instant
b: java.math.BigDecimal
---
letsPlot(simple.toMap()) { x = "a"; y = "b" } + geomLine()
```

The above Notebook works fine unless it depends on a library that pulls in the latest version of `kotlinx.datetime`.