feat(nix): expose per-version extension packages, catalog, and instance tools

Adds passthru.perVersion (version -> single-version derivation) to each
multi-version extension (18 files, one line each) -- the attrset already
existed inline as the buildEnv input, this surfaces it instead of
discarding it. No change to any buildEnv output or extension identity.

New flake-parts module nix/packages/extension-catalog.nix, exposing
(packages + legacyPackages):

- site-extensions-catalog-<major> (15/17/orioledb-17): pg-extensions-
  catalog.json mapping { ext -> { extversion -> store path } }, plus
  bin/{resolve,update} preset with PG_EXTENSIONS_CATALOG. Assembled at
  build time from the wrappers' control files, so keys are real
  extversions (pgsql-http nix "1.5.0" -> "1.5") and include
  sub-extensions (postgis_topology, plcoffee, ...). unsafeDiscardReferences
  keeps the closure to just the JSON (6.8 KiB, not 2.4 GiB).
- site-extensions-versions-<major> (legacyPackages): the generic
  single-version packages the catalog points at (lean, no multi-version
  buildEnv), so the CI matrix builds and caches them.
- Generic tools, one version each (not per-major): site-extensions-resolve
  (manifest json -> store paths), download-nix-store-paths (retry/timeout
  substitution, not extension-specific), site-extensions-update (chains
  both + nix-env --install --remove-all onto PROFILE, atomic).

Part of PSQL-1530.

Author: brainrake

nix/ext/hypopg.nix

@@ -98,6 +98,7 @@ buildEnv {
   '';
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit pname latestOnly;

nix/ext/index_advisor.nix

@@ -83,6 +83,7 @@ pkgs.buildEnv {
   ];
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit pname latestOnly;

nix/ext/pg-safeupdate.nix

@@ -83,6 +83,7 @@ pkgs.buildEnv {
   '';
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit pname latestOnly;

nix/ext/pg_cron/default.nix

@@ -116,6 +116,7 @@ buildEnv {
   };
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit switch-ext-version latestOnly;

nix/ext/pg_net.nix

@@ -145,6 +145,7 @@ pkgs.buildEnv {
   '';
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit pname latestOnly;

nix/ext/pg_partman.nix

@@ -100,6 +100,7 @@ pkgs.buildEnv {
   '';
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit switch-ext-version libName latestOnly;

nix/ext/pg_repack.nix

@@ -140,6 +140,7 @@ buildEnv {
   '';
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit pname latestOnly;

nix/ext/pg_tle.nix

@@ -111,6 +111,7 @@ buildEnv {
   '';
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit pname latestOnly;

nix/ext/pgaudit.nix

@@ -240,6 +240,7 @@ buildEnv {
   '';
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit pname latestOnly;

nix/ext/pgmq/default.nix

@@ -104,6 +104,7 @@ buildEnv {
   pathsToLink = [ "/share/postgresql/extension" ];
 
   passthru = {
+    perVersion = lib.mapAttrs (name: value: build name value.hash) versionsToUse;
     versions = versionsBuilt;
     numberOfVersions = numberOfVersionsBuilt;
     inherit pname latestOnly;