feat!: add temporal extension literals

[wackywendell]

Description

This PR adds first-class extension argument support for temporal typed literals, for example:

ExtensionLeaf:TemporalLiteralTest[
  created_at='2023-01-01T12:00:00':timestamp,
  watermark='2023-01-01T12:00:00.123456789':precisiontimestamptz<9>
  => value:string
]

Those arguments are represented as ExtensionValue::Literal(ExtensionLiteral) instead of a generic expression value. Extension handlers can still request them as Expr; the literal widens to a normal Substrait literal expression in that case.

Changes

• Added ExtensionLiteral, backed by substrait::proto::expression::Literal.
• Added temporal constructors such as date_days, time_micros, timestamp_micros, precision_time_units, precision_timestamp_units, and precision_timestamp_tz_utc.
• Added TryFrom<Literal> for ExtensionLiteral so the supported literal-kind policy lives with ExtensionLiteral, not in parser control flow.
• Split the grammar into typed_literal and untyped_literal so extension argument parsing can match typed literals directly.
• Kept unsupported typed literals such as 42:i16 as expression values.
• Added parsing and textification for precisiontime<N>, precisiontimestamp<N>, and precisiontimestamptz<N> literals, building on trunk's existing precision temporal type parser.
• Added extension roundtrip coverage for temporal literal arguments.

API Impact

This is a breaking change for extension handlers that expected temporal typed literal arguments to arrive only as Expr. Those values now arrive as ExtensionValue::Literal, but handlers can still request Expr through ArgsExtractor.

This also adds a new public extension argument type, ExtensionLiteral.

Validation

• cargo check
• just fmt
• just check
• cargo test --doc
• just test
• git verify-commit a185f25e237e 9bf90c0eb687