Support function expressions in table settings

[sharadgaur]

What

Allow table SETTINGS values to use expressions in addition to scalar literals.

This adds support for ClickHouse table-disk definitions such as:

SETTINGS disk = disk(
    type = 's3_plain_rewritable',
    endpoint = 'from_env OBJECT_STORAGE_ENDPOINT',
    readonly = true
)

It also supports nested disk definitions used by cached reader tables.

Why

The parser currently rejects function expressions in table settings:

unexpected token: "disk", expected <number>, <bool> or <string>

This prevents callers from parsing SHOW CREATE TABLE output for tables using s3_plain_rewritable and cache disks.

Validation

• go test ./... -count=1
• Added coverage for function and nested-function setting values

go vet ./... still reports the existing Formatter.WriteByte signature warning in parser/format.go.