proposal: time: add support for ISO 8601 duration format

[EricGusmao]

Proposal Details

This proposal suggests adding two new functions to the time package: one to parse the standard ISO 8601 duration format and another to format a time.Duration into an ISO 8601 string.

Problem

The standard library's time.ParseDuration function only supports a simple format (e.g., 1h30m) and cannot handle the widely-used ISO 8601 duration standard. This format is common in APIs, database systems, and configuration files.

Proposed Solution

This proposal suggests adding a parsing function and a formatting method. The names used here are illustrative and would be subject to discussion during the review process.

1. Parsing: A new function to parse the ISO 8601 duration string.

   func ParseISO8601Duration(s string) (time.Duration, error)

2. Formatting: A new method on time.Duration to return an ISO 8601 string.

   func (d time.Duration) ISO8601String() string

Benefits

• Standard Compliance: Aligns the time package with a major international standard used across the industry.
• Improved Interoperability: Simplifies working with other systems and services that produce or consume ISO 8601 durations.
• Enhanced Developer Experience: Provides a robust, built-in solution for a common task, removing the need for external dependencies or boilerplate code.