Micro_Rust_Std_Lib: add verified slice and vector operations

[nagyors]

Issue #17: Slice expansion.

Extends Micro_Rust_Std_Lib's StdLib_Slice.thy with a batch of verified slice and vector utility functions. Each new function follows the existing pattern, with crush/crush_base discharging the proofs.

Added:

• slice_swap / vec_swap — swap two elements by index
• slice_contains / vec_contains — membership test
• slice_copy_from_slice — overwrite a slice from another slice of equal length
• slice_reverse — in-place reversal
• slice_fill — fill a slice with a given value
• slice_split_at — split a list into two at a given index
• vec_push / vec_pop — push/pop on a fixed-capacity vector, returning Result/Option to signal capacity/emptiness
• slice_sort — in-place sort for linorder element types

Each is registered under micro_rust_notation so it's callable from µRust source using its Rust standard-library name (swap, contains, fill, push, pop, sort, etc.).

Test

Ran make build to ensure the project builds.

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