Add chainable constructor helpers to the AST

[jakub-id]

This is just an experiment to see how far we can get without the builder.

[jakub-id]

@adamdickmeiss it's a bit more tricky to use than the builder but much less magic and easier to pass around.

[Copilot]

Pull request overview

This PR adds chainable constructor helpers to the CQL AST package to enable direct construction of query trees without using the builder pattern. It's an experimental approach to simplify query construction.

Changes:

• Added constructor helper functions (Search, SearchRel, And, Or, Not, Prox, Bool) for building CQL clauses
• Added chainable With*/Add* methods on all AST types (Query, Clause, SearchClause, BoolClause, Sort, Modifier, Prefix)
• Added tests demonstrating the new API with complex nested boolean queries

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
cql/chain.go	Implements chainable constructor helpers and fluent methods for all AST node types
cql/chain_test.go	Tests core functionality with nested AND/OR queries, verifying correct serialization and precedence

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