Add unit tests for extractPath, extractHierarchy, and printHierarchy

[Copilot]

extractPath, extractHierarchy, and printHierarchy (introduced in #83) had no test coverage despite non-trivial logic around DN parsing, tree construction, and conditional formatting.

Tests added (ldap_test.go)

• Test_extractPath — covers normal DNs, empty string, missing =, trailing = (empty value filtered), = inside value, and whitespace trimming
• Test_extractHierarchy — covers empty SearchResult, single-entry tree construction, shared-ancestor deduplication across multiple entries, and malformed DN entries
• Test_printHierarchy — covers nil-safe behaviour, slash-path for non-CN nodes, colon-path for CN nodes with printNodesIfCN=true, and recursive child traversal

Example of path extraction edge cases exercised:

// Value containing '=' uses first '=' as separator
extractPath("CN=John=Doe,DC=com")
// → [{com DC} {John=Doe CN}]

// Trailing '=' is filtered (empty value)
extractPath("DC=com,OU=")
// → [{com DC}]

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