feat: fast provide support in dag import

[lidel]

Builds on #11046 to make fast-provide more practical (default behavior configurable via Import.* config) and supported in both ipfs add and ipfs dag import.

Fixes

Combined provide strategies didn't work

Strategy checking used else if, which breaks bitflag combinations like pinned+mfs:

// Before (broken):
if strategy&ProvideStrategyPinned != 0 && dopin {
    shouldProvide = true
} else if strategy&ProvideStrategyMFS != 0 && toFilesSet {  // never reached!
    shouldProvide = true
}

// After (fixed):
if strategy&ProvideStrategyPinned != 0 && dopin {
    shouldProvide = true
}
if strategy&ProvideStrategyMFS != 0 && toFilesSet {  // now works
    shouldProvide = true
}

New Features

Config defaults for fast-provide flags

Set defaults in config instead of passing flags on every command. See docs/config.md for Import.FastProvideRoot and Import.FastProvideWait options.

This way everyone can disable fast provide globally if it somehow negatively impacts their setup. This allows people to update to 0.39 without being blocked by any potential regression.

dag import support

dag import now supports --fast-provide-root and --fast-provide-wait flags. See updated ipfs dag import --help.

Refactors

• Extracted ExecuteFastProvide() to core/commands/cmdenv/env.go for code sharing
• Added ResolveBoolFromConfig() helper for flag/config resolution