refactor(util): migrate util/* SFINAE patterns to C++20 concepts

[DennisOSRM]

Issue

Closes #7534
Part of #7530

Replace enable_if / void_t / SFINAE patterns with requires clauses and standard C++20 concepts across four utility headers.

Changes

• alias.hpp: Replace std::enable_if_t<!std::is_same<...>> default template parameter with trailing requires(!std::is_same_v<ToAlias, FromNumeric>) on to_alias()
• filtered_integer_range.hpp: Replace std::enable_if<std::is_integral<Integer>::value> SFINAE parameter with requires std::integral<Integer>; replace now-unused <type_traits> with <concepts>
• indexed_data.hpp: Replace IsValueIterator alias template + dual-overload return-type SFINAE with a single adapt() function using requires std::same_as<...> for the iterator constraint and if constexpr for the string_view dispatch
• static_rtree.hpp: Replace template <typename = std::enable_if<Ownership == Container>> constructor SFINAE with trailing requires(Ownership == storage::Ownership::Container)

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Tasklist

• self-review code for correctness and following the coding guidelines
• add tests (existing unit tests cover all changed code paths)
• review
• adjust for comments

[Copilot]

Pull request overview

Refactors several include/util/* headers to replace SFINAE (enable_if, void_t) constraints with C++20 requires-clauses and standard concepts, improving compile-time diagnostics while keeping runtime behavior the same.

Changes:

• Constrains utility APIs using C++20 concepts (std::integral, std::same_as) and requires instead of std::enable_if.
• Simplifies IndexedDataImpl::adapt() into a single constrained template using if constexpr for std::string_view handling.
• Updates StaticRTree container-only constructor gating via a requires clause rather than a templated SFINAE parameter.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
include/util/alias.hpp	Replaces enable_if-based exclusion on to_alias() with a requires clause; minor formatting-only adjustments.
include/util/filtered_integer_range.hpp	Switches filtered_irange() constraint to requires std::integral<Integer> and updates includes accordingly.
include/util/indexed_data.hpp	Replaces iterator SFINAE + overload set with a single adapt() constrained by std::same_as plus if constexpr dispatch.
include/util/static_rtree.hpp	Replaces constructor SFINAE gating with requires(Ownership == storage::Ownership::Container); minor formatting-only adjustments.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.23%. Comparing base (b9d7303) to head (e20be43).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7632      +/-   ##
==========================================
+ Coverage   90.83%   94.23%   +3.40%     
==========================================
  Files         484      484              
  Lines       37816    37815       -1     
==========================================
+ Hits        34350    35635    +1285     
+ Misses       3466     2180    -1286     

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