upgrades sqlx from 0.7.4 to 0.8.6 to fix a critical security vulnerability
where encoding values larger than 4GiB could cause integer overflow in the
protocol length prefix, potentially allowing SQL injection at the protocol level.

vulnerability details:
- CVE: RUSTSEC-2024-0363
- affected versions: sqlx <= 0.8.0
- issue: binary protocol misinterpretation caused by truncating casts
- impact: possible SQL injection via protocol-level smuggling
- presentation: DEF CON 32 - "SQL Injection Isn't Dead"

fix included in sqlx 0.8.1+:
- added deny directives for clippy::cast_possible_truncation
- added deny directives for clippy::cast_possible_wrap
- added deny directives for clippy::cast_possible_loss
- manual audit and fixes for all flagged code

changes:
- update sqlx from 0.7 to 0.8 in Cargo.toml
- remove Cargo.lock from .gitignore (binary project needs reproducible builds)
- commit Cargo.lock to ensure exact secure versions are used

verification:
- all 110 tests passing
- release build successful
- no breaking API changes

references:
- https://rustsec.org/advisories/RUSTSEC-2024-0363
- launchbadge/sqlx#3441