Added three example changes in NEWS.Rd

[aakritixyz]

This PR implements the following three changes in the R source:
1. S4 object support for confint.default()
• confint.default() now works on S4 objects as long as suitable coef() and vcov() methods exist.

2.	substring() and substr() improvements
•	Both functions now accept i2 = NULL, allowing extraction until the end of the string.
•	Improves convenience and aligns with user expectations.

3.	Introduction of %notin% operator
•	%notin% added as a base R idiom for !(x %in% table)
•	Enhances readability and avoids repeated negation in user code.

Motivation:
• Enhance S4 object compatibility.
• Improve string handling convenience.
• Provide a cleaner syntax for common negation of %in%.

Impact:
• Backward compatible; no breaking changes for existing S3 workflows.

[bbolker]

Are you aware that this is a one-way mirror of the R code base, i.e. that pull requests here aren't noted by the R developers? The r-devel@r-project.org mailing list and the R bugzilla site (see https://www.r-project.org/bugs.html, search for "bugzilla") are the venues for contributions to R (also see discussion here about contributing)

[aakritixyz]

Thanks for clarifying! I understand now that this GitHub repository is a read-only mirror and that official contributions are handled via the R-devel mailing list or the Bugzilla site. I really appreciate the guidance and will follow the proper channels for any future contributions.

[bbolker]

FWIW %notin% was recently added to the development version of R:

• https://stat.ethz.ch/pipermail/r-devel/2025-November/084230.html
• https://stat.ethz.ch/pipermail/r-devel/2025-December/084243.html
• r-devel/r-svn@7101184

Your other two suggestions seem reasonable: I would introduce them (possibly as separate topics) to r-devel@r-project.org

[aakritixyz]

Thanks for the update! I appreciate you considering introducing my suggestions on r-devel@r-project.org. I’ll also read through the %notin% discussion to stay up to date.