feat(cat): implement GNU display flags (-A -b -e -E -s -t -T -v) (#293)

* test(cat): add comprehensive tests for -v nonprinting character display

Agent-Id: agent-b06ccde0-dadd-446a-8eb7-4da1a3a9a277
Linked-Note-Id: b2ce1141-e925-4ca2-9839-9929c05d6e05

* test(cat): add comprehensive comparison tests for display flags (-A -b -

Agent-Id: agent-cb21b343-b39f-4576-af13-6eca0dfea909
Linked-Note-Id: 2f16c18e-02bf-45f0-9c55-ea5a46c11175

* feat(cat): implement GNU display flags -A -b -e -E -s -t -T -v

Add show-nonprinting/-v byte table, show-ends, show-tabs, squeeze-blank, number-nonblank, long options, and -u no-op, matching GNU coreutils. Includes unit tests and locked comparison fixtures.

Signed-off-by: Lars Trieloff <lars@trieloff.net>

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Signed-off-by: Lars Trieloff <lars@trieloff.net>