feat: introduce Body type class and some Body types for HTTP

[algebraic-dev]

This PR introduces the Body type class, the ChunkStream and Full types that are used to represent streaming bodies of Requests and Responses.

This contains the same code as #10478, divided into separate pieces to facilitate easier review.

The pieces of this feature are:

• Core data structures: feat: add core HTTP data types #12126
• Headers: feat: introduce Headers data type for HTTP #12127
• URI: feat: introduce URI data type for HTTP #12128
• Body: feat: introduce Body type class and some Body types for HTTP #12144
• H1: feat: introduce HTTP/1.1 protocol state machine #12146
• Server: feat: introduce HTTP/1.1 server #12151
• Client:

[ghost]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 0a0323734b2d10c3f9355659f8e44b67bd36f644 --onto 4c1e4a77b4952098ea043f9b8c2d155c20b24523. You can force Mathlib CI using the force-mathlib-ci label. (2026-01-25 00:53:54)

[leanprover-bot]

Reference manual CI status:

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• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase 0a0323734b2d10c3f9355659f8e44b67bd36f644 --onto 75d7f7eb227bc54dc6ea3d8ead090ee4180debaf. You can force reference manual CI using the force-manual-ci label. (2026-02-10 02:04:52)
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