GH-46914: [C++][FlightSQL] Remove boost/algorithm/string.h dependency

[Reranko05]

Rationale for this change

Issue #46914 requests removing the remaining boost/algorithm/string.hpp dependency from FlightSQL.

What changes are included in this PR?

• Replace boost::iequals() with arrow::internal::AsciiEqualsCaseInsensitive()
• Replace boost::istarts_with() with a local case-insensitive prefix helper
• Remove boost/algorithm/string.hpp includes from sqlite_server.cc and test_app_cli.cc

Are these changes tested?

The modified files compile successfully in the local build configuration. CI will validate FlightSQL configurations.

Are there any user-facing changes?

No.

• GitHub Issue: [C++][FlightSQL] Remove boost/algorithm/string.h dependency #46914

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

cpp/src/arrow/flight/sql/example/sqlite_server.cc:24

• sqlite_server.cc uses std::strlen (see GetArrowType) but no longer includes <cstring> after removing the Boost header. Relying on transitive includes can break compilation on some platforms/toolchains; please include <cstring> explicitly.

#include <mutex>
#include <random>
#include <sstream>
#include <unordered_map>
#include <utility>

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit 11721e7.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details. It also includes information about 35 possible false positives for unstable benchmarks that are known to sometimes produce them.