Bump dependencies to current major versions

[rubenhensen]

Summary

Refreshes all dependencies before the first publish of the fork.

Crate	Old	New	Notes
reqwest	0.11	0.12	Major; existing API usage compat
thiserror	1.0	2.0	Major; #[from] / #[error] work
qrcode	0.12	0.14	Two majors; examples only
serial_test	0.5	3.2	Multiple majors; #[serial] works
serde	1.0.123	1.0	Minor refresh
serde_json	1.0.61	1.0	Minor refresh
url	2.2	2.5	Minor refresh
tokio	1.13	1.40	Minor refresh
tokio-test	0.4.2	0.4	Minor refresh

Also updates internal tests and examples to use irmars::... (the package was renamed from irma to irmars in the prior PR).

pg-core is the public re-export of reqwest::Error via Error::NetworkError(#[from] reqwest::Error), so consumers (postguard) that catch this variant will need their own reqwest = "0.12" bump for the types to align.

Test plan

• cargo build --tests --examples succeeds
• cargo test --lib -> 6 passed
• cargo fmt --check clean
• cargo clippy --all-targets shows only pre-existing warnings (not introduced here)
• Integration tests (RUN_INTEGRATION_TESTS=1) — require local irma server, not run in this PR

[dobby-coder]

Reviewed the diff and ran the suite locally.

Verified

• cargo build --tests --examples — clean
• cargo test --lib — 6/6 pass
• cargo fmt --all -- --check — clean
• Clippy CI job already green
• Diff matches the description: deps bumped, examples + integration tests switched from irma:: to irmars::

Notes

• reqwest 0.12 leaks into the public API via Error::NetworkError(#[from] reqwest::Error), as called out in the PR body. Downstream (postguard) will need a matching bump — that caveat is correctly flagged.
• thiserror 2.0 is a drop-in for the #[from] / #[error("…")] usage in src/error.rs; no syntax in this repo touches the breaking-change surface.
• qrcode 0.14 and serial_test 3.2 are only in dev-deps/examples and still compile/run.

Integration tests (RUN_INTEGRATION_TESTS=1) need a live irma server, so not run here — flagged in the test plan already.

LGTM, ready to ship before the first publish.