refactor(sdk-crypto): Room key sharing, introduce extensible strategy

[BillCarsonFr]

Fixes: #3562

Extracted the logic to collect the devices that should receive a room key.
Introduce a new CollectStrategy that will define how to sort devices that should receive the room_key and those that should receive a witheld code.

There is no functional changes in this PR, a following PR will introduce an IdentityBased strategy that will select devices depending on if they are signed by their owner.

• Public API changes documented in changelogs (optional)

Signed-off-by:

[codecov]

Codecov Report

Attention: Patch coverage is 79.03226% with 13 lines in your changes missing coverage. Please review.

Project coverage is 83.86%. Comparing base (b34a2cd) to head (ca6537b).
Report is 73 commits behind head on main.

Files	Patch %	Lines
...c/session_manager/group_sessions/share_strategy.rs	77.96%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3605      +/-   ##
==========================================
+ Coverage   83.84%   83.86%   +0.02%     
==========================================
  Files         253      254       +1     
  Lines       25884    25892       +8     
==========================================
+ Hits        21702    21714      +12     
+ Misses       4182     4178       -4     

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[poljar]

Left a small nit about our module convention, looks good otherwise.

[poljar]

Please run:

$ git mv crates/matrix-sdk-crypto/src/session_manager/group_sessions.rs crates/matrix-sdk-crypto/src/session_manager/group_sessions/mod.rs

to rename and move group_sessions.rs file into the group_sessions folder, we're using this module convention across all our crates. For more info about Rust modules check out: https://doc.rust-lang.org/reference/items/modules.html.

[BillCarsonFr]

Done

[poljar]

I think you need a small change in that file after it was moved, CI will let us know.

[richvdh]

Please do remember to update the changelog when landing changes like this.