feat: Implement THREAD

[coveralls]

Pull Request Test Coverage Report for Build 7680942201

• -26 of 343 (92.42%) changed or added relevant lines in 8 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.04%) to 93.059%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
imap-codec/src/codec/encode.rs	18	19	94.74%
imap-types/src/command.rs	0	1	0.0%
imap-types/src/response.rs	0	1	0.0%
imap-types/src/core.rs	0	3	0.0%
imap-codec/src/extensions/thread.rs	237	245	96.73%
imap-types/src/extensions/thread.rs	58	70	82.86%
<!--	Total:	317	343	92.42%	-->

Files with Coverage Reduction	New Missed Lines	%
imap-types/src/flag.rs	1	70.67%
imap-types/src/body.rs	2	39.47%
<!--	Total:	3		-->

Totals
Change from base Build 7608447919:	-0.04%
Covered Lines:	9546
Relevant Lines:	10258

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💛 - Coveralls