refactor!: rename ScanData to ScanMetadata

[zachschuermann]

What changes are proposed in this pull request?

Rename ScanData to ScanMetadata and Scan::scan_data to Scan::scan_metadata (and corresponding FFI). Additionally, renames TableChangesScanData to TableChangesScanMetadata. Additional docs/refactor coming in #768

This PR affects the following public APIs

breaking changes:

1. rename ScanData to ScanMetadata
2. rename Scan::scan_data() to Scan::scan_metadata()
3. (ffi) rename free_kernel_scan_data() to free_scan_metadata_iter()
4. (ffi) rename kernel_scan_data_next() to scan_metadata_next()
5. (ffi) rename visit_scan_data() to visit_scan_metadata()
6. (ffi) rename kernel_scan_data_init() to scan_metadata_iter_init()
7. (ffi) rename KernelScanDataIterator to ScanMetadataIterator
8. (ffi) rename SharedScanDataIterator to SharedScanMetadataIterator

How was this change tested?

existing

resolves #816

[codecov]

Codecov Report

Attention: Patch coverage is 70.37037% with 24 lines in your changes missing coverage. Please review.

Project coverage is 84.89%. Comparing base (8961e97) to head (a5269fb).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ffi/src/scan.rs	0.00%	16 Missing ⚠️
kernel/src/scan/mod.rs	80.00%	0 Missing and 3 partials ⚠️
kernel/src/table_changes/scan_file.rs	78.57%	0 Missing and 3 partials ⚠️
kernel/src/table_changes/log_replay.rs	80.00%	0 Missing and 1 partial ⚠️
kernel/src/table_changes/scan.rs	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #817      +/-   ##
==========================================
+ Coverage   84.87%   84.89%   +0.02%     
==========================================
  Files          83       83              
  Lines       20311    20316       +5     
  Branches    20311    20316       +5     
==========================================
+ Hits        17239    17248       +9     
+ Misses       2221     2219       -2     
+ Partials      851      849       -2     

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[nicklan]

nice. Just a few more places where we call this "scan data":

kernel/tests/golden_tables.rs
276:    let mut scan_metadata = scan.scan_metadata(&engine).expect("scan data");
292:    let scan_metadata: Vec<_> = scan.scan_metadata(&engine).expect("scan data").collect();

kernel/src/table_changes/scan_file.rs
81:/// for res in scan_metadata { // scan data table_changes_scan.scan_metadata()

kernel/src/table_changes/scan.rs
183:    /// deletion vectors present in the commit. The engine data in each scan data is guaranteed

ffi/src/scan.rs
178:/// Call the provided `engine_visitor` on the next scan data item. The visitor will be provided with

kernel/src/table_changes/log_replay.rs
30:/// Scan data for a Change Data Feed query. This holds metadata that is needed to read data rows.

ffi/examples/read-table/read_table.c
86:// For each chunk of scan data (which may contain multiple files to scan), kernel will call this
297:    print_error("Failed to construct scan data iterator.", (Error*)data_iter_res.err);
304:  print_diag("\nIterating scan data\n");
311:      print_error("Failed to iterate scan data.", (Error*)ok_res.err);
315:      print_diag("Scan data iterator done\n");

kernel/src/scan/state.rs
155:/// for res in scan_metadata { // scan data from scan.scan_metadata()

[sebastiantia]

looks good, found some neglected architecture doc that i had no idea existed

delta-kernel-rs/doc/architecture.md

Line 89 in 8961e97

ScanFileIterator --> ScanDataIterator