feat: pub deps -s mermaid

[tisohjung]

#4732

mermaid version of deps command
pub deps -s mermaid

below are the expected outputs from deps_test.dart

1. deps -s mermaid

          %% Dart SDK 3.1.2+3
          graph LR
            %% Root
            myapp["myapp 0.0.0"]

            %% Direct dependencies
            from_path["from_path 1.2.3"]
            normal["normal 1.2.3"]
            overridden["overridden 2.0.0"]

            myapp --> from_path
            myapp --> normal
            myapp --> overridden

            %% Dev dependencies
            unittest["unittest 1.2.3"]
          
            myapp -. dev .-> unittest

            %% Dependency overrides
            override_only["override_only 1.2.3"]
          
            myapp -. override .-> overridden
            myapp -. override .-> override_only

            %% Transitive dependencies
            circular_a["circular_a 1.2.3"]
            circular_b["circular_b 1.2.3"]
            dev_only["dev_only 1.2.3"]
            other["other 1.0.0"]
            shared["shared 1.2.3"]
            transitive["transitive 1.2.3"]

            %% Normal dependency chain
            normal --> circular_a
            normal --> transitive

            %% Dev dependency chain
            unittest --> dev_only
            unittest --> shared
          
            %% Circular dependencies
            circular_a --> circular_b
            circular_b --> circular_a
          
            %% Transitive chains
            transitive --> shared
            shared --> other
            other --> myapp

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3. deps -s mermaid --no-dev

          %% Dart SDK 3.1.2+3
          graph LR
            %% Root
            myapp["myapp 0.0.0"]

            %% Direct dependencies
            from_path["from_path 1.2.3"]
            normal["normal 1.2.3"]
            overridden["overridden 2.0.0"]

            myapp --> from_path
            myapp --> normal
            myapp --> overridden

            %% Dependency overrides
            override_only["override_only 1.2.3"]

            myapp -. override .-> overridden
            myapp -. override .-> override_only

            %% Transitive dependencies
            circular_a["circular_a 1.2.3"]
            circular_b["circular_b 1.2.3"]
            other["other 1.0.0"]
            shared["shared 1.2.3"]
            transitive["transitive 1.2.3"]

            %% Transitive chains from direct deps
            normal --> circular_a
            normal --> transitive

            %% Circular dependencies
            circular_a --> circular_b
            circular_b --> circular_a

            %% Transitive dependency chains
            transitive --> shared
            shared --> other
            other --> myapp

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