Adopt 8-bit ANSI option

[clipperhouse]

uax29 added an option for 8-bit control sequences. This PR adds support for that option in width calculations.

It turns out that Truncate with 8-bit escapes can lead to confusing outcomes, by concatenating bytes that, when combined, form a new UTF-8 codepoint. That’s bad. This was discovered by fuzzing. I’ve decided to have Truncate only respect the 7-bit option (which was the status quo). Better for the package to have a limitation than confusion.

[Copilot]

Pull request overview

This pull request adds support for 8-bit ECMA-48 control sequences by introducing a new ControlSequences8Bit option. This complements the existing ControlSequences option (which handles 7-bit sequences) and leverages the recently added 8-bit control sequence support in the uax29 v2.7.0 library.

Changes:

• Added ControlSequences8Bit field to the Options struct to enable zero-width treatment of 8-bit C1 control sequences (0x80-0x9F)
• Updated width calculation logic to treat graphemes starting with C1 control bytes as zero-width when the option is enabled
• Enhanced truncate functions to preserve both 7-bit and 8-bit trailing escape sequences based on the respective options
• Added comprehensive test coverage for 8-bit sequences, independence of 7-bit/8-bit options, and mixed scenarios
• Created separate options.go file to consolidate option definitions (refactoring)
• Created separate truncate.go file for truncation functions (refactoring)

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
options.go	New file containing the Options struct with the new ControlSequences8Bit field and DefaultOptions
width.go	Added C1 control byte detection for zero-width treatment; removed Options definition and truncate functions (moved to separate files)
truncate.go	New file containing truncation functions; updated to handle both 7-bit and 8-bit escape sequences with the new isEscapeLeader helper
graphemes.go	Updated to configure the grapheme iterator with AnsiEscapeSequences8Bit option
width_test.go	Added comprehensive tests for 8-bit sequences, independence tests, and regression test for truncation edge case
fuzz_test.go	Added 8-bit control sequences to fuzz test seeds and option combinations

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