Add more benchmarks for rust-enzyme

[bytesnake]

orthogonal changes to #1797

Adds

• FFT benchmark
• LSTM benchmark

iters=1048576
Adept real 0.151445 res=2.000000
Adept forward 10.001950 res=2.000000
Adept combined 11.013875 res'=1.000000
Tapenade real 0.157400 res=2.000000
Tapenade forward 0.151567 res=2.000000
Tapenade combined 0.698478 res'=1.000000
Enzyme real 0.151740 res=2.000000
Enzyme forward 0.155274 res=2.000000
Enzyme combined 0.716533 res'=1.000000
Enzyme (Rust) real 0.076485 res=2.000000
Enzyme (Rust) forward 0.078106 res=2.000000
Enzyme (Rust) combined 0.872660 res'=1.000000

    {   
        "batch-size": 1,
        "llvm-version": "17.0.6 (https://github.com/rust-lang/llvm-project.git 606bc11367b475542bd6228163424ca43b4dbdbc)",
        "mode": "ReverseMode",
        "name": "lstm_l4_c4096.txt",
        "tools": [
            {   
                "name": "Tapenade combined",
                "result": [
                    -0.008575290597839427,
                    -0.011735340558479943,
                    -0.015711794103922424,
                    0.013403993612214683,
                    -0.01716095951783106
                ],
                "runtime": 5.61006498336792
            },
            {   
                "name": "Adept combined",
                "result": [
                    -0.008575290597839427,
                    -0.011735340558479943,
                    -0.01571179410392242,
                    0.013403993612214683,
                    -0.01716095951783106
                ],
                "runtime": 16.16798973083496
            },
            {   
                "name": "Enzyme combined",
                "result": [
                    -0.857578932569891,
                    -1.1735362282316883,
                    -1.5712501573631974,
                    1.3404550989482777,
                    -1.716115266442339
                ],
                "runtime": 1.546381950378418
            },
            {   
                "name": "Enzyme (Rust) combined",
                "result": [
                    -0.8575792351173962,
                    -1.1735364473410599,
                    -1.5712502394962382,
                    1.3404540893143668,
                    -1.7161156338245582
                ],
                "runtime": 1.8011260032653809
            }
        ]
    }

[ZuseZ4]

@bytesnake, do you want to merge your branch into the main bench branch, now that these two work?

[ZuseZ4]

closing since merged into other bench branch.