Add more context to ms rules / identity provider callbacks

[mulmarta]

Maybe useful to know more context

Call-outs

Moving GroupContext to core means making tree_hash and confirmed_transcript_hash public (there's currently a function on ExternalGroup that returns confirmed_transcript_hash anyway).

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT license.

[tomleavy]

@mulmarta holding off on merging this for a week or so to see if we need any non-breaking changes first

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.91304% with 14 lines in your changes missing coverage. Please review.

Project coverage is 90.16%. Comparing base (9f4d07f) to head (431ba42).

Files with missing lines	Patch %	Lines
mls-rs-core/src/group/context.rs	57.89%	8 Missing ⚠️
mls-rs/src/group/mls_rules.rs	55.55%	4 Missing ⚠️
mls-rs-identity-x509/src/provider.rs	0.00%	1 Missing ⚠️
mls-rs/src/group/message_processor.rs	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #204      +/-   ##
==========================================
+ Coverage   90.14%   90.16%   +0.01%     
==========================================
  Files         175      176       +1     
  Lines       31498    31558      +60     
==========================================
+ Hits        28395    28453      +58     
- Misses       3103     3105       +2     

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[tomleavy]

I really like the direction of this! Left some comments

[mulmarta]

I fixed the merge conflict (version in Cargo.toml), I think I addressed all the comments, and we waited 2 weeks. OK to merge @tomleavy ?

[tomleavy]

I fixed the merge conflict (version in Cargo.toml), I think I addressed all the comments, and we waited 2 weeks. OK to merge @tomleavy ?

Yup, I think we are good