chore: bump proc-macro-crate to 2.0.0 in borsh-derive

[serprex]

Raise MSRV to 1.67

Enables getting latest toml crates in dependencies

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Edit: upgrading proc-macro-crate is useful with respect to supporting borsh package rename in workspace level
This is illustrated by sample repo

[dj8yfo]

@serprex please fix CI.
Or otherwise attach a short proof that minimal rust version has to be increased from 1.66 in order to support this change.

Please also provide a short memo in description, what the advantages for borsh lib of bumping proc-macro-crate from 1 to 2 are.

[serprex]

proc-macro-crate 2 MSRV is 1.66 according to their small version 2 release: bkchr/proc-macro-crate@39a7c18

I noticed rust_decimal pulling in old toml crate versions due to this

But, you're right & toml_datetime 0.6.5 raised their MSRV to 1.67

So I've fixed PR with MSRV being raised to 1.67, but understand rejecting this PR since my original assessment didn't involve raising MSRV

[dj8yfo]

@frol please take a look. I'll revert second commit if it's ok to bump msrv to 1.67

[dj8yfo]

TODO: fix link if the msrv is bumped to 1.67

[frol]

@dj8yfo Thanks for staying on guard for users of borsh and avoiding raising requirements unnecessarily. This change as of now is totally fine with me.