update resources faster with package_update

[wardi]

Fixes #5713

Proposed fixes:

1. selectively skip validation and dictization on resources if both are true:
   • dataset metadata is unchanged
   • skipped resource metadata is unchanged
2. skip updates completely if no metadata was changed
3. compare new and existing resource model objects before commit to avoid commit processing time
4. pass original_package in context from actions that call package_show with for_update=True to package_update to allow low-cost validated metadata comparisons

100-resource dataset action	old	new	improvement
resource_create	.721	.419	70%
resource_update	1.05	.445	130%
resource_delete	.709	.478	48%
package_resource_reorder	.697	.479	45%
package_patch	.660	.621	6% *
resource_patch	.746	.413	80%
package_revise (updating resource)	.787	.267	190%

* validation and dictization applied for all resources when any dataset field changes, we only save commit time

[!NOTE] This change will affect custom validation rules that access resource metadata from dataset or other resource validators:

• only the changed resources are passed to validation
• flattened data the validators receive won't include skipped resources

This change does not affect validation of resource fields that depend on package fields because the package fields are always available in flattened data

Features:

• [x] includes tests covering changes
• [ ] includes updated documentation
• [ ] includes user-visible changes
• [ ] includes API changes
• [ ] includes bugfix for possible backport