fix: prevent accessible_by from permanently overwriting shared rule conditions

[SAY-5]

What does this fix?

Calling accessible_by for one model class permanently overwrites rule.conditions on the shared Rule objects stored in the ability's @rules. A subsequent can? check for a different model that shares the same rule then uses the already-normalized conditions, which may reference associations that do not exist on that model, causing NoMethodError or wrong results.

Reproduction (from #876)

# Ability definition - rule applies to both Project and Activity
can :read, [Project, Activity], client: { id: current_client.id }

# Project belongs_to :client (direct)
# Activity has_many-through path to client via :project

# Step 1 - works fine before accessible_by is called
can?(:read, @project)  # => correct result

# Step 2 - triggers ConditionsNormalizer for Activity
# Rewrites rule.conditions from { client: { id: x } }
# to { project: { client: { id: x } } } on the SHARED Rule object
Activity.accessible_by(current_ability)

# Step 3 - now broken
can?(:read, @project)  # => NoMethodError: undefined method `project' for Project

Fix

ActiveRecordAdapter#initialize now maps @compressed_rules through Rule#dup before passing to StiNormalizer and ConditionsNormalizer. The dup gives each adapter its own copy of the rule shell, so conditions= assignments from the normalizers are local and never touch the originals in @rules.

@compressed_rules = base_rules.map(&:dup)

Tests

Added a regression spec to conditions_normalizer_spec.rb:

• Confirms rule.conditions is unchanged after accessible_by is called (object identity preserved)
• Fails without the fix (rule.conditions becomes the normalized form)
• Passes with the fix

All 305 examples pass (0 failures, 2 pending) across both defined and random order.

Closes #876