Cron merge

[jgarzik]

No description provided.

[Copilot]

Pull request overview

This PR merges cron functionality into posixutils-rs, implementing four POSIX utilities: at, batch, crontab, and crond. The implementation adds a new cron workspace package with shared job parsing logic and individual binaries for each utility.

Key Changes:

• Adds complete cron system implementation with job scheduling, daemon management, and user crontab editing
• Implements comprehensive timespec parsing for the at command with timezone support
• Includes integration tests for all utilities

Reviewed changes

Copilot reviewed 16 out of 18 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
Cargo.toml	Adds cron workspace member (duplicated entry needs fixing)
Cargo.lock	Registers new posixutils-cron package
README.md	Marks at and crontab as completed
lib/utils.tsv	Adds at and crontab utility entries
process/Cargo.toml	Removes batch binary (moved to cron package)
cron/Cargo.toml	Defines new cron package with four binaries
cron/lib.rs	Provides shared constants and job module
cron/job.rs	Implements cron job parsing and execution
cron/at.rs	Implements at command with extensive timespec parsing (2781 lines)
cron/batch.rs	Implements batch command for deferred execution
cron/crontab.rs	Implements crontab editor with permission checking
cron/crond.rs	Implements cron daemon with signal handling
cron/tests/*.rs	Comprehensive integration tests for all utilities
cron/test_files/at/cmd_for_job.txt	Test data file