Update tests: use %==% for strict equality and drop ::: for internal functions

[Copilot]

Two test anti-patterns fixed: loose == comparisons (which don't catch type mismatches) replaced with %==% (identical()), and unnecessary gglite::: access removed since testit already exposes package internals to tests.

Test changes (tests/testit/test-gglite.R)

• All == assertions → %==% (e.g. chart$layers[[1]]$type %==% 'point')
• length(...) == n → length(...) %==% nL (integer literals to satisfy identical())
• gglite:::build_config(), gglite:::g2_cdn(), gglite:::annotate_df() → direct calls

# Before
(length(chart$layers) == 2)
config = gglite:::build_config(chart)
(config$children[[1]]$type == 'interval')

# After
(length(chart$layers) %==% 2L)
config = build_config(chart)
(config$children[[1]]$type %==% 'interval')

Conventions update (.github/copilot-instructions.md)

Added two rules to the Testing Conventions section:

• Use %==% instead of == for strict equality
• Never use ::: in tests; testit exposes internal functions automatically