feat: add type class for replayable body types

[algebraic-dev]

This PR adds a Replayable type class that is useful for checking if some Body can be replayed in a redirect request.

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase b5f7399bf19d623b3a5171732f1b3e617cfac38f --onto c47a0c7cf035381a2bcdd4cdf2442782eb4a5214. You can force Mathlib CI using the force-mathlib-ci label. (2026-05-30 13:58:43)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase b5f7399bf19d623b3a5171732f1b3e617cfac38f --onto 9e0092d0f0ef62de06235b67023f4b6621151116. You can force Mathlib CI using the force-mathlib-ci label. (2026-06-05 14:39:28)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase b5f7399bf19d623b3a5171732f1b3e617cfac38f --onto d2f48db30713019241520218d0965227bbb64eed. You can force Mathlib CI using the force-mathlib-ci label. (2026-06-11 15:14:57)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase ab122a187d64224faf53004c9631f664b852bb96 --onto 659e8bb858995b0a1ada239c5b3819c8f8f2772f. You can force Mathlib CI using the force-mathlib-ci label. (2026-06-15 17:11:23)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase ab122a187d64224faf53004c9631f664b852bb96 --onto 4792cd22887c8b529a351f6563b693426ff2a8f8. You can force Mathlib CI using the force-mathlib-ci label. (2026-06-18 13:04:06)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase ab122a187d64224faf53004c9631f664b852bb96 --onto ab9722836dea9e2f5ca3157f14cc1460454b3a67. You can force Mathlib CI using the force-mathlib-ci label. (2026-06-23 12:56:48)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase d5790c1f088236fe67b52500ff87bce2c848b0bb --onto 3259610687883ec1ea48c481aba2469f2f83facf. You can force Mathlib CI using the force-mathlib-ci label. (2026-07-21 19:08:44)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase b5f7399bf19d623b3a5171732f1b3e617cfac38f --onto 803553a556fd82fa1060efb0c43eda542130cb16. You can force reference manual CI using the force-manual-ci label. (2026-05-30 13:58:45)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase ab122a187d64224faf53004c9631f664b852bb96 --onto 803553a556fd82fa1060efb0c43eda542130cb16. You can force reference manual CI using the force-manual-ci label. (2026-06-15 17:11:24)
• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase d5790c1f088236fe67b52500ff87bce2c848b0bb --onto 49ff95727f98d43984726b26742d17a1ceea9dd5. You can force reference manual CI using the force-manual-ci label. (2026-07-21 19:08:45)

[TwoFX]

Looks good, just one minor nitpick about documentation.