chore(deps): bump rand to 0.9.1, remove rand_core

[luisschwab]

Closes #32 (or do we want to keep that open until a new release?)

Changelog

• Bump rand to 0.9.1 and move it out of dev-dependencies.
• Remove rand_core: only rand_core was imported, but then we would use bitcoin::key::rand.
• Remove bitcoin::key::rand::thread_rng() in favor of rand::rng().
• Rename thread_rng() to rng(), gen_range to random_range.
• Import getrandom when the target is wasm32: it was necessary to create .cargo/config.toml as well (for context, see Stop forwarding getrandom's wasm features rust-random/rand#886).

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo +nightly fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[coveralls]

Pull Request Test Coverage Report for Build 15243190737

Details

• 35 of 37 (94.59%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 85.344%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
wallet/src/keys/mod.rs	2	4	50.0%

Totals
Change from base Build 15166368710:	0.0%
Covered Lines:	7273
Relevant Lines:	8522

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💛 - Coveralls