spannertag/v0.1.0

Initial release of the nested module github.com/apstndb/structfields/spannertag.

Port of the Cloud Spanner Go client's unexported spannerTag / spannerTagParser / fieldCache (value.go, as of cloud.google.com/go/spanner v1.91.0) exported as Tag / Parser / Cache, including the read-only column tag support introduced in v1.86.0 (googleapis/google-cloud-go#12895):

• spanner:"-" drops the field; spanner:"->" marks it read-only keeping the Go field name.
• Tags split on ; with the column name first; -> or case-insensitive readonly parts mark the field read-only, surfaced as Tag.ReadOnly via fields.Field.ParsedTag.
• Cache is the exported counterpart of the client's fieldCache, built on the root fields module.

This module versions independently of the root fields module because it tracks cloud.google.com/go/spanner releases. License: Apache-2.0 (upstream Copyright Google LLC).