Allow using JSON path in select results

[git-hulk]

This closes #187.

Before ClickHouse supported JSON type, the select result should have at most 3 fields(db.table.column), so it's good to represent it with ColumnIdentifier.

After introducing JSON type, the JSON path might have more 3 levels, and it's weird
to represent the JSON path with db.table.column. So this PR introduces Path for this
purpose. And yes, it will break user behaviors if using ColumnIdentifier.

[coveralls]

Pull Request Test Coverage Report for Build 17633065282

Details

• 20 of 34 (58.82%) changed or added relevant lines in 4 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.04%) to 50.425%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
parser/ast_visitor.go	0	1	0.0%
parser/walk.go	3	5	60.0%
parser/ast.go	10	21	47.62%

Files with Coverage Reduction	New Missed Lines	%
parser/ast.go	1	39.5%
parser/parser_table.go	1	66.23%

Totals
Change from base Build 17367436417:	0.04%
Covered Lines:	7416
Relevant Lines:	14707

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💛 - Coveralls

[Copilot]

Pull Request Overview

Replaces the ColumnIdentifier type with a new Path type to support JSON paths with more than 3 levels in ClickHouse select results. This change enables handling of nested JSON fields like a.b.c.d.e while maintaining compatibility with existing database.table.column paths.

• Introduces new Path type with a Fields array to handle arbitrary-length dot-separated paths
• Removes the ColumnIdentifier type that was limited to database.table.column structure
• Updates the AST walker, visitor pattern, and parser to support the new Path type

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
parser/walk.go	Adds Path case to AST walker and removes ColumnIdentifier case
parser/ast_visitor.go	Updates visitor interface to replace VisitColumnIdentifier with VisitPath
parser/ast.go	Replaces ColumnIdentifier struct with new Path struct implementation
parser/parser_table.go	Updates parser logic to create Path objects instead of ColumnIdentifier
parser/testdata/	Adds test cases and updates golden files to reflect the new Path structure

Comments suppressed due to low confidence (1)

parser/walk.go:1

• The condition logic is inverted - this should return false when Walk() returns false, not true. This will cause the walker to incorrectly stop traversal when it should continue.

package parser

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[Lance726]

LGTM.