[Store] Structure RedisConnectionConfig environment settings

[bitborne]

Description

Converges Mooncake Store's Redis connection environment settings under a private RedisConnectionConfig as part of #3809.

• Groups MC_REDIS_DB_INDEX, MC_REDIS_USERNAME, and MC_REDIS_PASSWORD in the common environment catalog.
• Resolves one config per Store Redis connection attempt and removes direct environment reads from the Redis connection business component, while keeping the public ConnectRedis() and ResolveRedisDbIndex() APIs unchanged.
• Preserves unset and empty DB index as database 0, decimal indices from 0 through 255, surrounding ASCII whitespace, a leading +, exact credential text, password-gated AUTH, optional ACL username, binary-safe %b commands, AUTH-before-SELECT ordering, existing error mapping, and Redis-disabled behavior.
• Keeps MC_REDIS_DB_INDEX string-typed in the catalog only to distinguish an explicitly empty value from a nonempty malformed value, then reuses the shared typed integer parser for nonempty input.
• Intentionally rejects non-integer prefixes and suffixes such as 1junk, 1e2, and 0x1, which the previous std::stoll call accepted by ignoring unconsumed text. The documented contract is an integer from 0 through 255, and the invalid-value path remains silent.
• Adds focused config, compatibility-wrapper, repeated-read, credential, error, and Redis-enabled business-path tests.

Open PR #1538 also touches these variables as part of a broad cross-module global Environ singleton migration. This PR is the narrow Store-only owner migration required by the current #3809 rules: it uses a component-owned private config, preserves Store diagnostics and per-connection lifecycle, adds direct RED-to-GREEN coverage, and leaves Transfer Engine and TENT readers unchanged.

The optional authentication, DB selection, binary-safe command, and ACL username behaviors established by #512, #1339, #1722, and #1757 remain unchanged.

Module

• Transfer Engine (mooncake-transfer-engine)
• Mooncake Store (mooncake-store)
• Reshard (mooncake-reshard)
• Mooncake EP (mooncake-ep)
• Mooncake PG (mooncake-pg)
• Integration (mooncake-integration)
• P2P Store (mooncake-p2p-store)
• Python Wheel (mooncake-wheel)
• Common (mooncake-common)
• Mooncake RL (mooncake-rl)
• CI/CD
• Docs
• Other

Type of Change

• Bug fix
• New feature
• Refactor
• Breaking change
• Documentation update
• Performance improvement
• Other

How Has This Been Tested?

Test commands:

cmake -S . -B build -DBUILD_UNIT_TESTS=ON -DSTORE_USE_REDIS=ON
cmake --build build --target redis_connection_config_test mooncake_store_master_objects -j32
ctest --test-dir build -N -R '^redis_connection_config_test$'
ctest --test-dir build -R '^redis_connection_config_test$' --output-on-failure
pre-commit run --files mooncake-common/include/environment_variables.h mooncake-store/src/CMakeLists.txt mooncake-store/src/config/redis_connection_config.h mooncake-store/src/config/redis_connection_config.cpp mooncake-store/src/ha/common/redis/redis_connection.cpp mooncake-store/tests/CMakeLists.txt mooncake-store/tests/redis_connection_config_test.cpp
./scripts/code_format.sh --check --changed-lines --base kvcache/main

Before the production change, the focused test passed the three preserved DB-index cases and failed the typed-contract regression for all three old prefix-acceptance inputs: 1junk, 1e2, and 0x1. After the change, the Redis-enabled config test passes, the Store master objects build successfully, all applicable touched-file pre-commit hooks pass with pre-commit 4.6.2, and the post-commit changed-lines check passes with clang-format 20.1.8.

Test results:

• Unit tests pass
• Integration tests pass (if applicable)
• Manual testing done (describe below)

Checklist

• I have performed a self-review of my own code
• I have formatted my code using ./scripts/code_format.sh
• I have run pre-commit on the files changed in this PR and all hooks pass
• I have updated the documentation (if applicable)
• I have added tests to prove my changes are effective
• For changes >500 LOC: I have filed an RFC issue

No documentation update is needed: the supported contract remains an integer DB index from 0 through 255, and the normalization only removes undocumented partial-number parsing.

AI Assistance Disclosure

• No AI tools were used
• AI tools were used (specify below)

Codex assisted with behavior and ownership inventory, compatibility analysis, implementation, focused RED-to-GREEN tests, verification, and pre-submission review. I reviewed every changed line and can defend the change end-to-end.