Drop Timex, bump HTTPoison 2.x, fix modern OTP builds

[kidbombay]

Summary

Modernizes dependencies and tooling so Cloudex builds on current Erlang/OTP (including OTP 28) and current Elixir, removes Timex from the signing path, upgrades HTTPoison to 2.x, and updates dev/test tooling and ExUnit. Cloudinary signing and HTTP usage stay the same from an API perspective, aside from using the standard library for the signing timestamp.

Motivation

• Timex was only used for a Unix timestamp in signed requests; :os.system_time/1 is enough and drops tzdata and other transitive weight.
• HTTPoison 1.x / older Hackney / ssl_verify_fun are problematic on newer OTP; HTTPoison 2.x tracks a supported Hackney line. An explicit ssl_verify_fun override avoids resolving 1.1.5, which fails to compile on OTP 26+.
• Dev/test dependencies are bumped so the project compiles without Mix/Elixir deprecation noise on recent toolchains.
• Config uses import Config / config_env() instead of deprecated Mix.Config.
• Tests run with async: true where appropriate; the env test restores CLOUDEX_API_KEY so the global environment is not leaked.

Changes

Area	Details
Runtime deps	Remove timex / tzdata. HTTPoison ~> 2.3. Optional jason unchanged. ssl_verify_fun ~> 1.1.7 override for safe resolution.
Elixir	Require ~> 1.11 (required by HTTPoison 2).
Cloudex.CloudinaryApi	Signing timestamp: :os.system_time(:second). JSON backend: Application.compile_env(:cloudex, :json_library, Jason).
Cloudex.Url	Doctest: charlist examples → strings ("auto", "progressive").
Config	import Config, import_config "#{config_env()}.exs" in config/config.exs; same pattern in dev / test / prod.
Mix	def cli/0 with preferred_envs (replaces deprecated preferred_cli_env in project/0).
Dev/test	Credo ~> 1.7, Dialyxir ~> 1.4, Mix.Test.Watch ~> 1.4, ExVCR ~> 0.17.
Tests	use ExUnit.Case, async: true on test modules; EnvOptionsTest uses on_exit to restore CLOUDEX_API_KEY.
Other	cloudex.iml: remove stale library entries for dropped deps.

Breaking changes

1. Elixir: minimum 1.11 (previously declared ~> 1.7 in mix.exs).
2. HTTPoison 2: downstream apps that pinned HTTPoison 1.x may need to move to 2.x. See HTTPoison — upgrading to 2.x.x (notably ssl vs ssl_override if you pass custom SSL options; Cloudex does not today).
3. Timex: anything that relied on Timex only as a transitive dependency of Cloudex must add Timex explicitly.

Testing

• mix compile
• mix test (including doctests)

Optional follow-ups (out of scope here)

• CHANGELOG + version bump for a Hex release.
• Document minimum Elixir / OTP in the README.