feat(tracker-core): widen mysql download counters to bigint (subissue 1525-07)

[josecelano]

Implements subissue 1525-07 of the persistence overhaul (#1525): align Rust and database types by widening only MySQL download-counter columns to BIGINT while keeping NumberOfDownloads = u32.

Spec: docs/issues/1721-1525-07-align-rust-and-db-types.md

Closes #1721.

Scope

• Add migration 4 for MySQL to widen:
  • torrents.completed -> BIGINT NOT NULL DEFAULT 0
  • torrent_aggregate_metrics.value -> BIGINT NOT NULL DEFAULT 0
• Add migration 4 for SQLite as a no-op to keep migration history aligned.
• Keep NumberOfDownloads as u32 (no u64 widening).
• Update SwarmMetadata.downloaded and downloads() to use the NumberOfDownloads alias.

Validation

• MySQL db-compatibility test path now verifies migration outcomes:
  • migration history count is 4
  • both target columns are bigint
  • round-trip works for 2_200_000_000_u32 (above i32::MAX)
• SQLite idempotency test now verifies _sqlx_migrations count is 4.
• cargo fmt --all
• linter all

[Copilot]

Pull request overview

Adds the next schema migration to widen MySQL download counters to BIGINT (while keeping the Rust domain type NumberOfDownloads = u32) and strengthens driver-level tests and documentation around the new type boundary.

Changes:

• Add migration #4: MySQL widens torrents.completed and torrent_aggregate_metrics.value to BIGINT; SQLite adds a no-op migration to keep histories aligned.
• Extend MySQL/SQLite driver tests to assert migration history count is 4 and validate MySQL round-trips a value above i32::MAX.
• Update SwarmMetadata.downloaded and downloads() to use the NumberOfDownloads alias and add/update the subissue spec doc.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/tracker-core/src/databases/driver/sqlite/mod.rs	Extends SQLite idempotency test to assert _sqlx_migrations count is 4.
packages/tracker-core/src/databases/driver/mysql/mod.rs	Extends MySQL compatibility test to assert migration count/type widening and round-trip above i32::MAX; adds column-type assertion helper.
packages/tracker-core/migrations/sqlite/20260409120000_torrust_tracker_widen_download_counters.sql	Adds SQLite no-op migration #4 to align migration history.
packages/tracker-core/migrations/mysql/20260409120000_torrust_tracker_widen_download_counters.sql	Adds MySQL migration #4 to widen counter columns to BIGINT.
packages/primitives/src/swarm_metadata.rs	Switches downloaded and downloads() to use NumberOfDownloads alias.
docs/issues/1721-1525-07-align-rust-and-db-types.md	Adds updated spec describing “widen DB only” design and validation strategy.
docs/issues/1525-overhaul-persistence.md	Updates EPIC step 7 spec link to the new spec filename.
docs/issues/1525-07-align-rust-and-db-types.md	Removes the old spec doc (superseded by the new 1721-... file).

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[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 36 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.79%. Comparing base (a370c3e) to head (d67efdd).
⚠️ Report is 6 commits behind head on develop.

Files with missing lines	Patch %	Lines
...ges/tracker-core/src/databases/driver/mysql/mod.rs	0.00%	35 Missing ⚠️
packages/primitives/src/swarm_metadata.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1722      +/-   ##
===========================================
- Coverage    80.89%   80.79%   -0.11%     
===========================================
  Files          348      348              
  Lines        25162    25208      +46     
  Branches     25162    25208      +46     
===========================================
+ Hits         20356    20368      +12     
- Misses        4579     4612      +33     
- Partials       227      228       +1     

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[josecelano]

ACK d67efdd