Move types to units

[tcharding]

Move the following unit types to the new units crate:

• locktime::absolute::{Height, Time}
• locktime::relative::{Height, Time}
• FeeRate
• Weight

Also move the parse module as well as constants as required.

Do minimal changes to get things building:

• Feature gate on "alloc" as needed.
• Remove rustdocs that use bitcoin types.
• Re-export units types so this is a non-breaking change.
• Fix import paths.

Patch 1 was originally #2526, putting it in via this PR to try and speed up the process.

Close: #2282

[coveralls]

Pull Request Test Coverage Report for Build 8241935679

Details

• 119 of 228 (52.19%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 84.159%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
bitcoin/src/blockdata/script/witness_version.rs	0	1	0.0%
bitcoin/src/blockdata/transaction.rs	2	4	50.0%
units/src/locktime/relative.rs	6	23	26.09%
units/src/parse.rs	28	50	56.0%
units/src/locktime/absolute.rs	66	133	49.62%

Totals
Change from base Build 8239659179:	0.1%
Covered Lines:	19540
Relevant Lines:	23218

---

💛 - Coveralls

[Kixunil]

FTR the "unit type" term in Rust refers to the () (empty slice/"void") type, so the title sounds a bit weird. :)

[tcharding]

Ah yes, of course - will change.

[sanket1729]

In future for PRs that move stuff, it might be useful to separate things in commits which we just copy pasting files (even if they don't compile) and the commits where you made changes to make things compile.

We can squash/fixup commits to make sure that each and every commit compiles.

[sanket1729]

ACK cbee978

[tcharding]

Thanks for the review @sanket1729, yeah I was a bit lazy on this one.

[tcharding]

Are you willing to review this as it is @apoelstra or do you want me to spit it up. If it matters I made minimal changes to get it to build, including IIRC:

• move the parse file and fix macro exports and fully qualified paths (feature gate on "alloc")
• cutn'pasta the Height/Time stuff
• cutn'pasta the LOCK_TIME_THRESHOLD
• move the weight, and fee_rate files
• remove the actual-serde attribute stuff
• fix the path when calling the parse macros
• fix prelude stuff
• cutn'pasta unit tests as appropriate
• Add and use error constructor for TimeOverflowError
• delete rustdoc that mentions LockTime from newly create units modules

Phew, now I write that it does seem a lot in one commit. But the only logical way to break it is to do parse and locktimes as one commit and then do Weight and FeeRate as another commit - but that will not make it all that much easier to review.

Requesting special consideration to just review as is - pretty please :)

[apoelstra]

ACK cbee978 lgtm. this is a good start. I think the LockTime types should follow Height and Time