Add numeric rounding value initialisation in test.data.table() (#6103)

* Add setNumericRounding(0) initialisation

Add setNumericRounding(0) initialisation and restore user's value on exit.

* Add test file for testing test.data.table()

Add test file for testing setNumericRounding(0) initialisation in test.data.table().

* Add test for numeric rounding initialisation in test.data.table()

* Add item for numeric rounding initialisation in test.data.table()

* Remove trailing whitespace on two lines

* Remove new test

Remove new test as requested by @MichaelChirico, to avoid nesting a test of test.data.table() in a script run by test.data.table().

* Delete inst/tests/issue_6082_tests.Rraw

Delete inst/tests/issue_6082_tests.Rraw because the test that used it was removed.

* Update NEWS.md

Move test.data.table() numeric rounding initialisation item from Bug Fixes to Notes as requested by @MichaelChirico.

NEWS.md

@@ -84,6 +84,8 @@
 
 12. `print.data.table` now honors `na.print`, as seen in `print.default`, allowing for string replacement of `NA` values when printing. Thanks @HughParsonage for the report and @joshhwuu for the fix.
 
+13. `test.data.table()` now initialises the numeric rounding value to 0 using `setNumericRounding(0)` to avoid failed tests if the user has set a different value, [#6082](https://github.com/Rdatatable/data.table/issues/6082). The user's value is restored on exit. Thanks to @MichaelChirico for the report and for describing the solution, and @markseeto for implementing.
+
 # data.table [v1.15.0](https://github.com/Rdatatable/data.table/milestone/29)  (30 Jan 2024)
 
 ## BREAKING CHANGE

R/test.data.table.R

@@ -79,6 +79,9 @@ test.data.table = function(script="tests.Rraw", verbose=FALSE, pkg=".", silent=F
   # sample method changed in R 3.6 to remove bias; see #3431 for links and notes
   # This can be removed (and over 120 tests updated) if and when the oldest R version we test and support is moved to R 3.6
 
+  userNumericRounding = getNumericRounding()
+  setNumericRounding(0)  # Initialise to 0 in case the user has set it to a different value. Restore to user's value when finished.
+
   # TO DO: reinstate solution for C locale of CRAN's Mac (R-Forge's Mac is ok)
   # oldlocale = Sys.getlocale("LC_CTYPE")
   # Sys.setlocale("LC_CTYPE", "")   # just for CRAN's Mac to get it off C locale (post to r-devel on 16 Jul 2012)
@@ -215,6 +218,8 @@ test.data.table = function(script="tests.Rraw", verbose=FALSE, pkg=".", silent=F
   suppressWarnings(do.call("RNGkind",as.list(oldRNG)))
   # suppressWarnings for the unlikely event that user selected sample='Rounding' themselves before calling test.data.table()
 
+  setNumericRounding(userNumericRounding)  # Restore the user's numeric rounding value
+
   # Now output platform trace before error (if any) to be sure to always show it; e.g. to confirm endianness in #4099.
   # As one long dense line for cases when 00check.log only shows the last 13 lines of log; to only use up one
   # of those 13 line and give a better chance of seeing more of the output before it. Having said that, CRAN