fix: annotate float literals so the build is clean on Rust 1.97

[ayozetr]

cargo clippy --all-targets --locked -- -D warnings, the exact command in both CI jobs, fails on whatever dtolnay/rust-toolchain@stable currently resolves to (1.97.1) with 32 instances of:

falling back to `f32` as the trait bound `f32: From<f64>` is not satisfied

They are calls like Stroke::new(1.0, arc_border()), where the parameter is generic and an unsuffixed float literal no longer resolves the way it used to. rustc still accepts it but announces a future hard error, and -D warnings promotes it to a build failure today — so the job goes red on every PR regardless of what the PR touches.

I ran into this on the Linux job. The Windows one runs the identical command, and 27 of the 32 sit in theme.rs and widgets.rs, neither of which has any cfg(windows), so I would expect the same there — worth confirming, since I have no Windows machine to check on.

Mechanical change (1.0 → 1.0_f32) produced by cargo fix, which is where all 32 suggestions came from. Verified clean under 1.95 and 1.97 on Linux.

Sending this one on its own and first, since anything else lands red without it. Context in #8.

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[ayozetr]

Heads-up on the red CI here, since it reads as "these patches are broken" and that is not what happened.

All six PRs got a CI run on 12 Aug that failed with no jobs executed at all:

CI: No jobs were run

The workflow was triggered, no runner was ever assigned, and the run was marked failed — so nothing was checked out, built or compiled. The API reports zero jobs on each of the six runs. That points at something on the runner or Actions-configuration side rather than anything in the branches, and it would presumably hit any fork PR the same way. You can see more of that than I can from outside.

For what it is worth, each branch passes cargo clippy --all-targets --locked -- -D warnings and cargo test on 1.95, and all six merge cleanly against main with one commit each.

This PR specifically I have just re-checked against 1.98.1, today's stable and what dtolnay/rust-toolchain@stable now resolves to: clippy clean, no warnings. The fix still does its job on the current toolchain.

One thing worth knowing if the runs ever do start: the other five will genuinely fail until this one lands. They branch off main and carry the 32 float-literal warnings this PR fixes — I checked one of them against 1.98.1 just now and clippy stops with exactly those 32. That is why this went out first and on its own. Once it is in I will rebase the rest.

Happy to rebase, split or drop any of them — just say which.