feat: Update content automatically (e.g. datetime fields on save)

[riodelphino]

Update content automatically, based on predefined rules.
Toggles enable/disable this function on demand, by :ZkUpdateToggle command.

For example (on save):

• Auto updating datetime fields in YAML
• Sort tags in YAML
• Change tags style from block to flow in YAML

(e.g.) Update datetime field in YAML frontmatter on save

Before:

---
modified : 2025-01-01 00:00:00
---

After (on save):

---
modified : 2025-11-23 12:31:12
---

modified field is automatically updated to current date and time.

options for above:

  ...
  update = {
    enabled = true,
    triggers = {
      on_save = {
        enabled = true,
        event = 'BufWritePre',
        rules = {
          ["Update datetime in YAML (modified as 2025-01-01 00:00:00)"] = {
            scope = "line",
            pattern = "^(modified *: *)(%d%d%d%d%-%d%d%-%d%d %d%d:%d%d:%d%d)$",
            format = function(captures, line)
              captures[2] = os.date("%Y-%m-%d %H:%M:%S")
              return table.concat(captures)
            end,
            in_yaml = true,
            notebook_paths = {},
            dirs = {},
          },
        },
      },
    },
  },
  ...

• in_yaml:
  true = only search in YAML
  false = only search in content
• dirs:
  valid directories (relative to notebook root). {} allows all directories.
• notebook_paths:
  valid notebook_paths. {} allows all notebook_paths.

Command

:ZkUpdateToggle toggles enabled.
:ZkUpdateToggle "on_save" toggles only on_save trigger.

Issues

• Slow down on saving a long file.

Notes

Cannot use zk.api.list or lyaml to get YAML information for the following reasons.

• BufWritePre requires sync process. (BufWriteCmd may not ?)
• The last change has not yet been caught by zk.index or lyaml.
• Ensure to keep the order of tags in YAML. (They break the order.)

Please give me feedback, also whether this PR should be another plugin or included in zk-nvim.

[riodelphino]

Somehow zk.txt and README.md were contaminated from my main branch (which merged all my un-merged PR).
So I cleaned up these unintended lines in latest three commits.

[riodelphino]

Added Example Rules

• Sort tags (on save)
• Change tags style from block to flow (on save)

[github-actions]

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