## Problem

When users run \`mix igniter.install ash_feistel_cipher\`, the
Spark.Formatter plugin was being applied to their entire project,
causing unwanted formatting changes to non-Ash code (e.g., migrations).

Example unwanted changes:
\`\`\`elixir
# Before
add :id, :uuid
create unique_index(:users, [:email])

# After (unwanted)
add(:id, :uuid)
create(unique_index(:users, [:email]))
\`\`\`

## Solution

Remove \`import_deps\` and \`plugins\` from \`.formatter.exs\` while
keeping the \`export\` configuration intact.

This ensures:
- ✅ ash_feistel_cipher DSL functions (source, target, bits, key, etc.)
can still be used without parentheses
- ✅ User projects' existing formatter settings remain untouched
- ✅ Only the necessary \`locals_without_parens\` configuration is
exported

## Changes

- Removed \`import_deps: [:spark, :reactor, :ash]\`
- Removed \`plugins: [Spark.Formatter]\`
- Kept \`export: [locals_without_parens: ...]\`