refactor: Give enum-from-int functions the ability to report errors.

[iphydf]

These functions are a bit clearer and don't need to change if enum values change.

See TokTok/hs-tokstyle#212 for the relevant linter implementation.

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This change is 

[codecov]

Codecov Report

Attention: 134 lines in your changes are missing coverage. Please review.

Comparison is base (19d8f18) 69.90% compared to head (4e603bb) 69.90%.

Files	Patch %	Lines
toxcore/tox_unpack.c	14.49%	118 Missing ⚠️
toxcore/Messenger.c	40.00%	9 Missing ⚠️
toxcore/group_pack.c	77.77%	4 Missing ⚠️
toxcore/events/conference_invite.c	0.00%	1 Missing ⚠️
toxcore/events/conference_message.c	0.00%	1 Missing ⚠️
toxcore/events/file_recv_control.c	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2475      +/-   ##
==========================================
- Coverage   69.90%   69.90%   -0.01%     
==========================================
  Files          75       75              
  Lines       25964    25999      +35     
==========================================
+ Hits        18150    18174      +24     
- Misses       7814     7825      +11     

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[JFreegman]

Reviewable status: 0 of 1 approvals obtained (waiting on @iphydf)

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toxcore/group_chats.c line 1283 at r3 (raw file):

    len_processed += sizeof(uint8_t);

    group_voice_state_from_int(voice_state, &shared_state->voice_state);

since these functions return bool do we want to log failures?

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toxcore/Messenger.c line 785 at r3 (raw file):

        default: {
            *out = USERSTATUS_INVALID;

I'm not 100% sure this should be the default. Maybe just setting it to NONE would prevent cascading failures?

[JFreegman]

Reviewed 5 of 7 files at r2, 12 of 12 files at r3, all commit messages.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @iphydf)