feat: upgrade to substrait 0.63 and migrate extension URIs to URNs

[EpsilonPrime]

PR 1 of a stack upgrading substrait-textplan to the latest substrait protos, then switching to substrait-packaging.

What

Bump the substrait crate 0.61 → 0.63 and the proto submodule to the matching spec commit (spec 0.85.0 / 2aaae7c0). The 0.63 protos remove the deprecated SimpleExtensionURI message and the extension_uris / extension_uri_reference fields in favor of SimpleExtensionURN / extension_urns / extension_urn_reference, so this migrates all URI handling to URNs.

Changes

• Converter/printer/parser switched from extension_uris → extension_urns and SimpleExtensionUri → SimpleExtensionUrn; FunctionData.extension_uri_reference → extension_urn_reference.
• Grammar: the extension_space token now accepts URN strings (extension:<owner>:<id>) which contain : — the old fragment-based URI token couldn't tokenize them.
• Visitor generator: disambiguate leaf names that now collide because NamedTable, PrecisionTimestamp, PrecisionTime and IntervalCompound each exist in two message scopes (via NAME_OVERRIDES).
• Printer: add not-yet-implemented arms for the new Lambda / LambdaInvocation expressions and Func type — full support lands later in the stack.
• Fixtures: migrate all TPC-H roundtrip fixtures and the q6 converter fixture from yaml URIs (/functions_X.yaml) to URNs (extension:io.substrait:functions_X).

Tests

All 48 tests pass (cargo test); cargo fmt --check clean.

[EpsilonPrime]

Missing / stubbed features introduced in this PR (for later decisions)

The URN bump pulled in new 0.63 proto types that this PR only stubs (they compile and round-trip, but have no textplan syntax and emit *_NOT_YET_IMPLEMENTED when printed):

• Lambda / LambdaInvocation expressions — new higher-order-function exprs; printer returns LAMBDA_NOT_YET_IMPLEMENTED / LAMBDA_INVOCATION_NOT_YET_IMPLEMENTED.
• Func type — the higher-order function type; print_type returns FUNC_TYPE_NOT_YET_IMPLEMENTED.
• Type aliases — type_alias_reference is not surfaced; the type-level Alias prints ALIAS_TYPE_NOT_YET_IMPLEMENTED.

These need a text-syntax design + fixtures to implement fully. Deferred per the stack plan; PR #17 lists the full consolidated gap list.