Restore lang_lambdas from Puppet 5.4 archive

[miharp]

Scope

Restores docs/_openvox_8x/lang_lambdas.md from the
puppetlabs/docs-archive (puppet/5.4).

Changes

Full content restored covering:

• Location — where lambdas can and cannot be used
• Syntax — parameter list structure with example, including optional/extra-arguments parameters
• Parameters and variables — positional passing, data type validation, mandatory vs optional
• Behavior — resource uniqueness, lambda-produced values, lambda scope, Callable data type

Adaptations from archive source:

• Prose Puppet → OpenVox where describing runtime behavior
• Removed Kramdown class tags ({:.concept}, {:.section})
• Replaced inpage anchor syntax with standard Markdown anchor link
• 4-space sub-list indents → 2-space (MD007)
• Lines wrapped to 210 chars (MD013)

Test plan

• bundle exec jekyll build succeeds with no errors
• markdownlint-cli2 reports 0 errors against the project's planned 210-char config
  (see #30)

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