Resolves the directory holding the compiled inflection data.

Inflection data is optional: when it has not been downloaded, inflection functions return {:error, %Localize.InflectionDataNotAvailableError{}} rather than raising. Three configuration forms are recognised, following the locale-cache convention (see Localize.Locale.Provider.locale_cache_dir/0):

# 1. Recommended. Resolved as
#    `Application.app_dir(:my_app, "priv/localize/inflection")`
#    at every read, so it computes the right path in mix
#    tasks and in releases.
config :localize, otp_app: :my_app

# 2. :otp_app plus a *relative* :inflection_data_dir,
#    resolved against the app's runtime root.
config :localize, otp_app: :my_app, inflection_data_dir: "priv/i18n/inflection"

# 3. An absolute :inflection_data_dir for fully custom
#    locations.
config :localize, inflection_data_dir: "/var/lib/localize/inflection"

Without configuration the directory defaults to the localize dependency's own priv/localize/inflection.

The data version segment

Artifacts live in a subdirectory named for Localize.Inflection.Provider.data_version/0, mirroring the CDN layout the same version addresses, so the configured directory holds one subdirectory per data version:

priv/localize/inflection/ae92d425e57a-r3/de.etf

The segment makes an artifact of an earlier data version unreachable rather than merely detectable: it is never the file a later version reads, so dir/0 is empty after a version bump and the data downloads afresh. Recording the version inside each artifact instead, as the locale cache does in Localize.Locale.Provider.Cache.stale?/1, would mean decoding the file to learn whether to read it, and an inflection artifact reaches 11 MB where a locale file stays near 1 MB.