Problem: CpPlatformOverrides lacked a template field and merge_lang()
never copied ov.template into the effective language config, so
per-platform template overrides were silently dropped.
Solution: add template? to CpPlatformOverrides and forward it in
merge_lang(), matching how extension is handled.
Problem: output comparison used exact string equality after whitespace
normalisation, causing correct solutions to fail on problems where
floating-point answers are accepted within a tolerance (e.g. 1e-6).
Solution: add an optional ui.panel.epsilon config value. When set,
actual and expected output are compared token-by-token: numeric tokens
are compared with math.abs(a - b) <= epsilon, non-numeric tokens fall
back to exact string equality. Per-problem epsilon can also be stored
in the cache and takes precedence over the global default.
Problem: new solution files were always created empty, requiring users
to manually paste boilerplate or rely on editor snippets that fire
outside cp.nvim's control.
Solution: add an optional template field to the language config. When
set to a file path, its contents are written into every newly created
solution buffer before the setup_code hook runs. Existing files are
never overwritten.
Problem: tbl_deep_extend merges user platforms on top of defaults, so
all four default platforms survive even when the user only configures a
subset. The picker then shows platforms the user never intended to use.
Solution: before the deep merge, prune any default platform not present
in the user's platforms table. This preserves per-platform default
filling (the user doesn't have to re-specify every field) while ensuring
only explicitly configured platforms appear.
