docs(`forge test`): improve description of `--flamechart` and `--flamegraph`, explaining the difference

[zerosnacks]

Component

Forge

Describe the feature you would like

The current description is not very descriptive

$ forge test --help

      --flamegraph
          Generate a flamegraph for a single test. Implies `--decode-internal`

      --flamechart
          Generate a flamechart for a single test. Implies `--decode-internal`

A flame graph is used to visualize which functions or operations within the smart contract are consuming the most gas overall in a sorted manner.

A flame chart shows the gas usage over time, illustrating when each function is called (execution order) and how much gas it consumes at each point in the timeline.

In both cases the measured value is gas consumption

The note about implies --decode-internal should persist

cc @zemse please correct me if I'm wrong

Additional context

Follow up of #8640