feat(sequences): sequence CRUD and sequence email management

[imjohnbo]

Part 2 of 8. Base: #14.

What this adds

Sequence CRUD:

kit sequences get <id>
kit sequences create --name <name> [...]
kit sequences update <id> [...]
kit sequences delete <id>

Sequence emails, nested under sequences:

kit sequences emails list <sequenceId>
kit sequences emails get <sequenceId> <id>
kit sequences emails create <sequenceId> --subject <s> --delay-value <n> --delay-unit <days|hours>
kit sequences emails update <sequenceId> <id> [...]
kit sequences emails delete <sequenceId> <id>

list and get accept --include stats. emails list also accepts --include-content.

Design notes

The update commands send only the fields that the user names. An update therefore never wipes a field by accident. The tests cover this.

The CLI validates send days, send hour, delay unit, and ID lists before it sends the request. A bad value reads as a CLI error instead of a 422.

validateNumericId rejects zero. Send hour and email position both allow zero. This branch adds validateIntInRange and validateEnum to the client for those cases.

Review notes

Tests: 147 before, 198 after. The 51 new tests assert the exact request for every new command.

Closes #6
Part of #4
Part of #7

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The stack

Merge from the top down. Each part builds on the one above it.

	PR	Contents
1	#14	Client query support and shared helpers
2	#15 (this one)	Sequence CRUD and sequence emails
3	#16	Posts and snippets
4	#17	Broadcast filters, account-wide stats, link clicks
5	#18	Subscriber slim listing, warnings, filter
6	#19	Tag rename, remove-by-email, bulk delete
7	#20	Account endpoints and purchase create
8	#21	Spec coverage map and its tests

Base branch: main for part 1, the previous part's branch for the rest.
GitHub retargets each base to main as the part below it merges.