The setterName() extension function now requires a symbolProvider parameter.
Updated call sites to pass the correct symbolProvider.

Verifies that structures with a 'meta' field get properly renamed to
'meta_value' with corresponding setter/getter methods to avoid conflicts
with error metadata fields.

Use setterName() extension function instead of manually constructing
setter names to handle field renaming (e.g. default -> default_value).

The previous approach renamed every member that the symbol provider
touched, which changed `set_default`/`set_build`/`set_builder` (and the
matching getters) for any struct with those fields — a breaking change
flagged by @rcoh on review.

The duplicate-definition bug only occurs for error-struct builders,
where `ErrorGenerator` injects `set_meta` for `ErrorMetadata`. Only
rename members whose raw name is `meta` and leave every other setter
and getter at its pre-existing `set_<raw>` / `get_<raw>` name.

Rewrite the regression test to actually reproduce the original bug: it
now builds a `TestError` (an `@error` shape with a `meta` member) and
asserts `set_default` stays intact, so the earlier failure mode and the
guard against unrelated renames are both covered.

Also drop a now-unused `toSnakeCase` import in `ServerBuilderGenerator`
that surfaced after rebasing onto main.