Add Virama conjunct for the Brahmic scripts

[jquast]

Brahmic script has conjuncts that "collapse" to cell width, Closes #155

(From specs.rst)

Virama Conjunct Formation

In Brahmic scripts, a Virama (Indic_Syllabic_Category=Virama in
IndicSyllabicCategory.txt) between two consonants triggers conjunct
formation: the font engine merges the consonants into a single ligature glyph.

• A Consonant immediately following a Virama contributes 0 width.

• The conjunct still occupies cells — the next visible advance settles it:

  • A following Mc (Spacing Combining Mark_, e.g. a vowel sign) counts as
    1 cell and closes the conjunct — no extra cell is added.
  • A following wide character (or end of string) adds 1 cell for the conjunct
    before counting its own width.

• Chains work the same way: C + virama + C + virama + C collapses each
  virama+consonant pair.

• Mn marks do not break conjunct context within the same aksara_.

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing jq/conjuct-formation (f113ee7) with master (38d03a5)}

Summary

✅ 60 untouched benchmarks
🆕 4 new benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
🆕	test_width_brahmic_bengali	N/A	2.3 ms	N/A
🆕	test_width_brahmic_devanagari	N/A	2.8 ms	N/A
🆕	test_wcswidth_brahmic_devanagari	N/A	2.6 ms	N/A
🆕	test_wcswidth_brahmic_bengali	N/A	2.1 ms	N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (38d03a5) to head (f113ee7).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #204   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           15        15           
  Lines          938       986   +48     
  Branches       239       247    +8     
=========================================
+ Hits           938       986   +48     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jquast]

I wasn't certain and made some errors along the way, but I integrated with latest master branch of ghostty through ucs-detect, and, they now match 100% for all language tests in the next ucs-detect release with this branch. I can't read these languages to know whether it is legible, but I can tell you that this matches ghostty behavior exactly, and probably also kitty and others, to be tested soon