need to deprecate binary_codec_sv2 and restructure binary_sv2 + derive_codec_sv2

[Shourya742]

The current structure of binary_sv2 does not follow best practices. Typically, a crate defining a proc_macro only includes an additional crate for the macro’s implementation. However, in binary_sv2, we have two separate crates—one for the proc_macro implementation and another for the primitives required for macro scaffolding. Due to the tightly coupled nature of the proc_macro implementation with the module structure, restructuring it requires rewriting some parts of the macro to align with the proposed design.

Kudos to @plebhash for pointing this out and suggesting a better structure: #1459 (comment)

[plebhash]

one detail coming from #1459 that we should clean up here is some leftover lifetime parameters that were originally motivated by serde support:

reference: 3f80718#r1947844273

[Shourya742]

Reimplement or redesign parts of proc_macro in derive_codec to work around bugs like this: #1468 (comment).

[plebhash]

this will introduce breaking changes to binary_sv2 APIs