Add `preferredPrefix` Support

[iObject]

Allow ROPM modules to declare a preferredPrefix in their package.json ropm config block. When ROPM installs such a module, it should use the declared prefix instead of deriving one from the package name or scope — unless the user has explicitly provided an alias at install time.

Currently, ROPM derives a module's prefix from its package name or npm scope (e.g. @rokucommunity/promises → rokucommunity_promises). This works fine for most cases, but module authors often know a cleaner, shorter, or more idiomatic prefix that downstream consumers should use. Without a way to declare this preference, every consumer ends up with verbose, auto-derived prefixes — and namespace rewrites inside .brs files reflect those verbose names.

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Desired Behavior

When a module author wants to suggest a prefix, they add a preferredPrefix field to the ropm config in their package.json:

{
  "name": "@rokucommunity/promises",
  "ropm": {
    "preferredPrefix": "promises"
  }
}

During ropm copy, ROPM should:

1. Detect the preferredPrefix field in the installed module's package.json.
2. Use that value as the module's prefix instead of the auto-derived one.
3. Apply the prefix consistently: folder naming under roku_modules/, and all namespace rewrites inside copied .brs and .xml files.
4. Log clearly that the preferred prefix was found and is being used.

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Alias Override Rule

If the user provided an explicit alias at install time, the preferredPrefix must be ignored entirely. The user-supplied alias always takes precedence.

Example — alias wins:

npm install mypkg@npm:@rokucommunity/promises
# ropm should use "mypkg", not "promises"

Example — preferredPrefix wins (no alias):

npm install @rokucommunity/promises
# ropm should use "promises" (from preferredPrefix), not "rokucommunity_promises"

The alias detection logic should compare the local package name against the resolved package name to determine whether an alias was explicitly provided.

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Logging

ROPM should emit informative output during copy so users understand why a non-default prefix is being used:

• When preferredPrefix is found and used: indicate that the default prefix was overridden by the module's declared preference.
• When an alias is present: use the alias silently (current behavior — no change needed).

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Acceptance Criteria

• preferredPrefix in a module's package.json ropm config is respected during ropm copy.
• Files are copied into roku_modules/<preferredPrefix>/ when preferredPrefix is active.
• Namespace strings inside copied .brs files are rewritten to use the resolved prefix.
• A user-supplied install alias overrides preferredPrefix.
• If preferredPrefix is absent, existing default/scoped prefix behavior is unchanged.
• Unit tests cover: preferred prefix used, alias overrides preferred prefix, no preferred prefix (regression).
• Output logging makes the prefix resolution decision visible to the user.