(WIP) feat: migrate pgrx extensions to crane build system

[yvan-sraka]

This change adds crane support to the existing pgrx extension builder, enabling better incremental build performance and caching for pg_jsonschema and other pgrx extensions. Crane separates dependency builds from main crate builds, allowing dependencies to be cached independently.

The unified buildPgrxExtension.nix now accepts an optional craneLib parameter. When provided, it uses crane's two-phase build (buildDepsOnly + buildPackage). Otherwise, it falls back to rustPlatform.buildRustPackage. Both paths share the same build and install logic, avoiding code duplication.

Crane requires Cargo.lock at the source root while rustPlatform accepts external lockFile paths. The builder handles this by ensuring external lock files are properly accessible during the build process. Crane's cargoVendorDir is only used for crane builds to avoid conflicts with rustPlatform's cargo handling.

Extensions opt into crane builds by passing useCrane = true to mkPgrxExtension. All existing build parameters remain compatible with both backends.

[samrose]

this one seems pretty important and would like to get to this one soon after nixpkgs update

[yvan-sraka]

pg_graphql (with useCrane = true) hits a tokio-postgres compilation error:

error: builder for '/nix/store/80sbdnbf97j3wjiy38vwi0w9y8qj41l2-pg_graphql-deps-deps-1.2.0.drv' failed with exit code 101;
       last 25 log lines:
       >     Checking tracing-error v0.2.1
       >    Compiling semver v0.11.0
       >     Checking tokio-util v0.7.4
       >     Checking pgx-sql-entity-graph v0.7.1
       >     Checking futures-executor v0.3.26
       >     Checking tokio-postgres v0.7.8
       >     Checking futures v0.3.26
       >    Compiling rustc_version v0.3.3
       >    Compiling atomic-traits v0.3.0
       >     Checking clap v4.1.6
       > error[E0277]: `DataRowBody` doesn't implement `std::fmt::Debug`
       >    --> /nix/store/v7hfg1lha0s198amava5m9gfqqpj9vk1-vendor-cargo-deps/c19b7c6f923b580ac259164a89f2577984ad5ab09ee9d583b888f934adbbe8d0/tokio-postgres-0.7.8/src/row.rs:202:5
       >     |
       > 199 | #[derive(Debug)]
       >     |          ----- in this derive macro expansion
       > ...
       > 202 |     body: DataRowBody,
       >     |     ^^^^^^^^^^^^^^^^^ `DataRowBody` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
       >     |
       >     = help: the trait `std::fmt::Debug` is not implemented for `DataRowBody`
       >     = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
       >
       > For more information about this error, try `rustc --explain E0277`.
       > error: could not compile `tokio-postgres` (lib) due to 1 previous error
       > warning: build failed, waiting for other jobs to finish...
       For full logs, run 'nix log /nix/store/80sbdnbf97j3wjiy38vwi0w9y8qj41l2-pg_graphql-deps-deps-1.2.0.drv'.
error: 1 dependencies of derivation '/nix/store/f8gq25rp5z9g14k5kbgsil4k4clhbdv5-pg_graphql-1.2.0.drv' failed to build
error: 1 dependencies of derivation '/nix/store/07fiwlxlzk4vpa5b57b6kzyj9nw696ma-pg_graphql.drv' failed to build

Basic crane integration works correctly (pg_jsonschema builds successfully) but crane uses the external Cargo.lock files directly while rustPlatform was applying patches that contained e.g. fixed dependency versions. Here, the external Cargo.lock files have tokio-postgres 0.7.8 which has this debug trait issue.

To fix this, we need to either update the external Cargo-X.X.X.lock files with compatible dependency versions or apply the same patches that rustPlatform was using.