Parameterization type fixes; use parameters instad of arms where appropriate

[esantorella]

Summary: Sometimes benchmarking code creates Arms from parameters just so they can be passed to a function that expects an Arm but only uses its parameters. This is silly. It's better to just have the function expect parameters.

Also updated some method signatures to use Mapping to indicate that they do not mutate the parameterization, which unfortunately creates the need for Pyre-fixmes if they are passed to a function or class such as Arm that does not annotate its arguments as immutable.

Differential Revision: D63327381

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This pull request was exported from Phabricator. Differential Revision: D63327381

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.68%. Comparing base (a144287) to head (e1b7f3b).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2780 +/- ## ========================================== - Coverage 95.68% 95.68% -0.01% ========================================== Files 488 488 Lines 47985 47984 -1 ========================================== - Hits 45915 45914 -1 Misses 2070 2070 ```

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This pull request was exported from Phabricator. Differential Revision: D63327381

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D63327381

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D63327381

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D63327381

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D63327381

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This pull request has been merged in facebook/Ax@6899783ddbbcd92f5114c908b56959e1dd83cbc7.